I wish to apologize in advance. I started writing this and the thoughts just kept flowing. I truly hope that what I wrote here is helpful in your skoolie journey, and will be helpful to others as well.
I think this is a good idea, and you wouldn't be the first authors to do something like this.
There are lots of good examples of people living full time on the road in an RV of some sort (skoolie or coach or commercially built RV, or whatnot). Technomadia, the RV Geeks, and many others do this every day. Heck, the Gypsy Journal couple published a newsletter on the road for years, before they settled in Florida and Nick started writing books faster than rabbits reproduce.
Bus size is going to be a very personal choice. There are merits and detriments to every size, and it's about meeting your own needs.
Smaller busses are typically built on a van cutaway chassis. Thing Chevrolet G30, P30, GMC 3500/4500/5500, ford E350/E450/E550, etc. They vary in length, tend to have well supported drivelines that most auto shops can handle, and come in steel body or fiberglass body options. You'll want to steer clear of specific powertrains. The ford 6.0L powerstroke is one example of an engine that is potentially very problematic, and often found in this size chassis. These designs approximately equate to a class C motorhome. I think they go up to around 25/26 feet long, tend to drive like a van, and are relatively easy to maneuver for someone used to driving a van or car.
Mid size busses come in a larger range. These tend to be conventional aka dog nose busses, but Bluebird made some really cute front engine flat nose busses in this size range. Think more of the 22-30 foot range.
Full size busses tend to be in the 30-40 foot range.
OTR motor coaches tend to be in the 40-45 foot range. OTR = Over The Road, think greyhound or charter bus. I don't have much specific knowledge of these, but still drool over them.
Some choose midsize or shorter busses because they want to do a lot of camping in state and national parks which may not accommodate a 40' rig.
So the choices you are looking at boil down to these:
: What one needs for a weekend or week away camping, vs what one needs for 2 or 3 months living and working on the road vs what one needs for full time living and working on the road are a huge spread. "epic road trip" funded by "dispatches from the road" sounds a lot like the 1-3 months living and working on the road type setup, but only you can answer that.
When you buy a bus from the rust belt, it can lead to a LOT of extra work just remediating the rust damage. Pretty much Virginia and north. Any place they salt the roads in the winter and still run the school busses when it snows. Georgia tends to close rather than risk going out in 1/4" of snow where Ohio people might go to school in 20" of snow. It's worth seeking a bus from the western US or southwest, even some of the midwest.
Gas vs Diesel
. There are good and bad engines in each type. For your smaller rigs, a big gas engine may make a lot more sense than a diesel engine found in that class rig, especially if you dislike the smell of diesel, or getting it on your hands when pumping.
. Manuals can still be found, but are rather rare. For an automatic, you're most likely to end up with an Allison. The AT545 is an older 4 speed without lockup torque converter. If you intend to do a lot of mountain driving, especially the western mountains, this is probably not the transmission for you. For relatively flat land, and not towing, this is a decent transmission. It was designed for a lot of stop and go bus routes, not sustained highway driving in mountains or towing things. The MT643 is the older 4 speed with lockup. You typically find the 545 and 643 on busses from the 80s and 90s. The Allison 2000 and 3000 series transmissions are very good transmissions, with lockup. Some of the 2000 series are 6 speed, some are 5 speed. Many of the 3000 series are 6 speed. The MD3060 is commonly found in larger busses, with 6th speed locked out. There's a way to enable it for another overdrive gear. Transmission swaps are doable, but require a lot of labor and cost. It's best to get the one you want on the first try. Unlocking 6th gear if available can give you a higher top speed, which means better economy at regular speeds.
. Do you want a short bus? can you put up with each other living and working in approximately 100-150 square feet of space day in and day out? Maybe a midsize bus is better for you. Or perhaps you want more space to spread out, and opt for a full size, or even an OTR coach. There's an awesome build in the coach build section for a van hool OTR coach, by offgr1d, which is spectacular. There's a beautiful MCI for sale on here right now for 6K, with some really cool geek cred to it, already stripped and ready for converting.
. You have hydraulics or air brakes. When you exceed a certain GVWR, you're pretty much guaranteed to have air brakes. Some states require a CDL for this, some require an air brake endorsement, or a class B non-CDL. The biggest non-technical thing to know about the differences is that hydraulic brakes fail in a "can't stop" mode, and air brakes fail in a "brakes locked up" mode. So if your hydraulic lines fail, you better downshift and seek a way to get stopped without brakes. If your air lines fail, you probably need a spatula to scrape your face off the windshield. Air brake systems have a primary and secondary air tank that takes up some space under your bus, something to keep in mind. It's not a lot of space, but it needs to be reachable to service them.
. Many busses aren't geared well for highway running, especially those in the flatter parts of the country. Mountain busses tend to have better gearing, and western busses as well. This is changable after purchase, but not cheap to do. Unfortunately, most busses do not list the rear end gear ratio, so that part is a bit of a crap shoot. That's why people recommend busses from Colorado, Utah, New Mexico, Nevada, Arizona, etc.
There is a book, The Bus Converter's Bible, that covers a lot of things. Build threads and discussion threads here are full of lots of useful information.
Before getting into a bus conversion, you should think of it as a multi-part problem you're trying to solve.
First, you're buying a used vehicle, with all the potential problems of that. Things might break. You might need to do serious remediation work to the chassis, driveline, etc to make it safe and keep it safe. Or, you might find a hidden gem. You will see ads touting "fleet maintained" like that's a huge benefit. Many school bus fleets are maintained by underpaid people that are always understaffed, with shoestring budgets, and the mechanics are under pressure to "get it back on the road quickest" instead of "safest" or "most correctly". As a personal point of reference, avoid busses from Montgomery County, MD. They literally grab whatever hardware is handy to reassemble things, not the correct bolts. And they are in the salt belt, the busses end up with a lot of rust and corrosion.
Second, you are embarking on a full home renovation project. Where you first have to strip out the school bus personality before getting to the point you can build a home foundation and a home inside your bus.
Third, when you do it yourself, you need to become proficient in the trades. Construction, insulation, electrical (120/240V AC as well as 12 or 24 or 48V DC systems), heating, air conditioning, plumbing... all the skills are needed. You can hire out various parts of course.
None of this is meant to discourage you. Converting a bus is a journey in itself, and can be very rewarding, and is pretty much guaranteed to also be very frustrating at times.
The diesel engine preferences tend to be the Cummins 8.3L, the DT466E (and NOT the Maxxxforce DT), and the Cummins 5.9L. The Mercedes Benz engine tends to be avoided. That might change when more people have it and find out all its gotchas. Many prefer the older busses for staying with a purely mechanical driveline. Others like the computer controlled engines.
The Caterpillar 3116 and 3126 engines are meh-level OK engines. However, as I was reminded by a friend this weekend, they're typically treated as disposable engines. It is frequently cheaper to toss the engine and replace it than to repair it properly. I have the 3126 in my current bus, and I'll make the best of it. My next bus will have something different, either the Cummins 8.3, or the DT466E, or something better if enough time has passed that something better is now out there.
Automatic transmission preferences tend to go 3000 series, then 2000 series, then 643, then 545. Note: many of the cutaway van chassis models, and things like the kodiak topkick chassis models, may or may not have an Allison. It's a good idea to run any configuration past the people here for opinions. We have opinions here, plenty to spare.
Length of bus is entirely subjective. Different lengths for different needs.
Built in A/C is a good thing if you intend to drive in the summer in hot areas (the south or southwest especially), as it tends to work much better than something like a mini split system when under way.
Flat nose vs conventional nose: Again, personal preference. A flat nose tends to have more usable living space vs a conventional for the same overall length.
Front engine vs rear engine. Rear engines only come in flat nose, and tend to look the most like a conventional expensive class A motorhome. The engine makes noise and heat when operating. Do you want it near you when driving, or far away? The amount of heat transferred to the living space can be mitigated, and noise dampening products can be used. A front engine allows for a door at the rear of the bus, and a rear engine negates that. Both have merit. A front engine flat nose bus will have the driver sitting over or somewhat forward of the front axle, and a rear engine bus is likely to have the driver sitting more forward of the front axle. This is due to balancing the power plant weight across the axles, and probably varies by chassis manufacturer. A front engine bus has a longer drive shaft, making it more difficult to have pass-through (side to side) compartments under the bus.
Bus bodies. There are a lot to look at just in the school bus arena. Thomas, Blue Bird, Carpenter, International/AmTran, just to name a few. Each has their own quirks. Blue Bird tends to have about 1/3rd the weight of the bus just in steel rivets. Thomas has slanted inward windows, and come in 3 different roof heights (low, mid, high, look behind the driver area, if it drops, it's low, if it's flat, that's mid, and if it rises, that's a high top). I've seen international rear engines busses where the back of the bus has this strange V design box things for engine reasons.
Newer busses starting sometime in the later 2000s might also be using multiplexed electrical signaling, which can be a can of worms all its own. A single wire can connect to multiple switches and control multiple functions based on a combination of resistances. As wires get corroded, those values can change. Removing things from the circuit can change the values. It is something that can be worked with with the appropriate level of knowledge, but it's something you might have to take a crash course in. Something as "simple" as removing the 8 way flashing lights can render your bus inoperable.
Once you get your bus, you start to deal with the things that are common to all bus conversions.
Seats need to be removed. Floors should be removed to assess potential rust damage. Ceiling panels can be removed. Adding insulation is recommended. Some like to remove the windows and cover over, and add RV type or house type windows. Others love the light of the bus windows, and work hard to seal them (some succeed) and make thermal curtains for them to help keep out the heat and cold when needed.
Some do a roof raise to gain more volume inside, and make it easier to add insulation without affecting headroom.
Then you start getting into floor plans. When laying out your plan, remember that plumbing is likely to go into tanks under the floor, so you need to know what is under your bus that might be in the way.
Once you figure out where everything should go, it's a good idea to tape it out and play with it a while to make sure it works for you.
Then you start your build.
For electrical, there are a lot of ways to go. Trying to stick to standard RV or Marine practices makes sense, because you can easily reuse things meant for those types of installations. Additionally, sticking to home wiring basics also makes sense for the same reasons.
Solar is one place where a skoolie tends to deviate from home stuff, and even most RVs.
You should start by enumerating the things you wish to run, and figure out how many watt-hours they use per day. Then figure out your highest current draw items you want to be able to power on at the same time. Figure out how many days you want to be able to operate without being able to get a full charge. Many hate generators, but when you have 2 straight weeks of rain, a generator can keep your batteries topped up with just a few hours run time per day.
Once you figure out your power needs, then you can start sizing your system appropriately. A bigger bus means being able to put more solar panels on the roof vs a smaller bus. It also means being able to have a heavier battery bank.
Power needs are 2 part. First, there's total watt hours. Second, there's peak current draw or peak wattage draw. Watts = volts times amps. Amps measure current, watts measure power. I'm simplifying here.
You need an inverter capable of handling your maximum simultaneous load with a small bit of reserve left. So if peak wattage usage is 3000, then a 3500 watt or higher inverter would make sense.
You need a battery bank with enough amp-hours to handle your total watt hours. If you need to use 4,000 watt hours per day, and handle 4 days without sun, then you need 16,000 watt hours of capacity. Remember, watts = volts times amps. Batteries are rated in amp hours, not watt hours. You can set up your battery bank as a 12, 24, or 48 volt system. Technically, there are many available voltage configurations, but these are the 3 most common in RV and Marine use, and you can easily find commodity hardware to work with them. So, divide your watts by volts to get the number of amp-hours you need accessible
. Notice that I said accessible. See, most batteries cannot be drained down too far before significantly reducing their life expectancy. This varies by chemistry, and you need to consult the battery manufacturers specs for the actual numbers. For some batteries, you may only be able to pull it down 15% or 25%. If we assme you need 16,000 watt hours of capacity, in a 24 volt bank, and can only discharge the bank 25% without damaging it, then we take 16,000 / 24 * 4 to get our answer. That's 2,666 amp hours approximately. If we could discharge the batteries to 50% State of Charge (SoC), then we could get away with 1,333 amp hours of battery bank.
For the record, that's an astounding amount of battery, and will take a lot of money and space and add a lot of weight.
Lead acid are the cheapest and easiest to deal with, and have been around forever. You can get them as flooded aka wet cells, as absorbed glass mat (AGM), or as gel cells (commonly used in UPS systems and alarm systems, not great for a large number of charge cycles). Then there's Lithium Ion batteries. And the top of the line are the Lithium Iron Phosphate LiFePo and Lithium Iron Phosphate Magnesium aka LMP batteries. They are much lighter weight, more energy dense, handle charge/discharge cycles better, can be discharged further, and cost a lot more. They also require individual cell battery management systems to keep one cell from being killed within the battery pack. That sounds scary, but really it is the state of the art right now, and there's a ton of info out there on it. Also, there are several commercial companies making battery banks for this.
If you have gotten this far, congratulations, you have not panicked yet.
The numbers given above show a very high energy consumption level. This was done for a reason. Look at your electric bill. See how many kilowatt-hours you used, and divide by the number of days you were billed for. a kilowatt-hour is 1,000 watt hours. Assuming a perfect battery bank capable of 100% discharge, 1 kilowatt hour is 83.3 Amp hours at 12V, 41.6 Amp hours at 24V, and 20.83 Amp hours at 48V. In your house, where you have 120V/240V setup, you're looking at 8.3 Amp hours for 120V, or 4.16 Amp hours at 240V. Having a 120V or 240V battery bank gets very expensive very fast, but the grid is relatively cheap.
This helps to hammer home the fact that in a stick and brick house, we are extremely wasteful of energy. My own apartment, which is quite efficient for a stick-and-brick structure, I used 773 kilowatt-hours of energy in 28 days, for an average of 27.6 kilowatt-hours per day. Compare this to the 16 kilowatt-hours over 4 days in my ridiculously oversized example above. I use almost double that in each day! For one person!
Typical household equipment is NOT efficient. Every item you have plugged in increases your power needs. Learning to be aware of this is a step along the way to reducing the amount of energy you need to live comfortably on the road. One way is to move to another energy source where possible. Propane for heat, cooking, and hot water makes a lot of sense. Buying super efficient appliances can help. For example, an "inverter" type microwave or compressor (air conditioner, fridge, freezer) can result in lower peak power use and lower overall power use. Rather than being On or Off, they can ramp up and down as needed. This isn't to be confused with a DC to AC inverter you would need to drive house circuits with battery power. LED DC powered lighting, DC powered fans, and other methods of energy reduction are also helpful.
Better insulation = less energy needed to heat or cool = lower energy budget.
Small changes on the thermostats make a huge difference.
Once you figure out your energy budget, one you can hopefully live within, you'll know how big to size your inverter and your battery bank, and probably recognize that you'll want to either plug into shore power at times to augment the solar, or run a generator at times. Nobody wants to run a generator 24/7, and a decently designed system won't make you do that.
You should decide how many watts of continuous duty you need from your inverter, as well as how many peak watts you need. A 3000W inverter can peak at up to 4500W depending on design, for just a second or a few seconds. A sustained draw will shut it down or burn it out or trip a breaker.
I generally recommend a 12V battery bank up to about 3000 watts. 24 up to around 5000 watts, and 48 for higher watts. The reason is the cable size needed to connect the inverter to the battery goes up dramatically as you have more current to pull.
3000 watts at 12 volts is 250A. 5000 watts at 12V is 416.6A (way too much to be running through a single wire sustained).
5000 watts at 24 volts is 208.3A. 5000 watts at 48 volts is 104A.
Higher voltage battery banks require more complexity, more management, and a little more TLC. But, they are still something most people can handle. It all boils down to finding the best answer for you. These are my guidelines, and your mileage may vary as they say.
Now, for your situation specifically.
Putting myself in your shoes as best I can, from the little bit I've read that you've posted, it sounds like you already have a preference towards a smaller bus.
I'm going to assume for a minute that "epic road trip" does not mean live in full time, and is probably more for a few weeks to a few months on the road.
You'll want a bedroom, bathroom, kitchen/galley, office space, and lounging space. You can be really creative with space, and make some spaces multi-functional. For example, your lounging space could double as some office space. Your bedroom could also double as some office space with a bit of creativity. You can keep the bathroom minimal with a small sink, toilet, and shower, perhaps making it a wet bath (everything gets sprayed by the shower, and you have to hide the TP before showering). The galley can be simple and small. Carrying some folding tables, chairs, and a camp stove, you can do much of your living outdoors. I recommend carrying a small screen house as well, to avoid the bugs. This will help a smaller space be less claustrophobic.
But you'll also want to think about the rainy days. How will you both work in the same space those days? Will you need more elbow room? Will you need your office spaces at opposite ends of the bus? Things to think about.
I'd be inclined to suggest one of the longer short busses, perhaps in the 24-30 foot range. Either a shuttle bus (fiberglass body) or even a shorter mid-sized conventional. Put in a small bathroom, make your kitchen small, make your living room double as dining room and office space, perhaps a bed that raises and lowers so you can have more living space underneath it. Some small tanks, some solar panels, and a 12V battery bank, with 300-500AH of capacity. A smaller 2500 to 3000 W inverter, and a portable inverter generator for those days you just don't get enough sun. A 12 volt cooler fridge, and another one for your freezer, running straight from the batter bank. Get used to using your propane stove for making coffee via a french press, instead of an electric coffee maker. Fill a thermos for the day, rather than having a large carafe.
You can go more minimal with a composting toilet, and using showers at truck stops, campgrounds, and fitness centers. That depends on your personal taste of course.
Hammocks are a great way to add lounging space in open areas without cluttering up the space. They can also be used for sleeping.
There is a lot of information in this post, meant to help you refine and define the solution you are seeking.
Good luck, and I look forward to seeing what you accomplish!