The major benefit of LiFePO4 over LiIon cells is ruggedness. That, and a pack made up of LiFePO4 cells may remain fully charged with no issue while a LiIon pack should not be stored at full charge for any appreciable period of time. The downside of the former (LiFePO4) is they're rated at 3.2V/cell versus 3.6V/cell so you're going to need to check your math at the margins.
Now let me help put ruggedness into context. I'm a model builder (RC model aircraft). We use packs made up of both types of cells, plus one more, LiPo (3.7V/cell). Moreover, we routinely charge/discharge them at higher rates than in RV-use. Higher rates just means we're more abusive of them. This is good in terms of learning dos and don'ts.
Note 1 - while I would never recharge a LiIon pack whilst mounted within a model (balsa, foam, fiberglass construction, think great tinder for starting a fire if you're a Boy Scout), I routinely will recharge mounted LiFePO4 packs. Why one and not the other? Greatly reduced fire risk with LiFePO4 cells compared to LiIon (and hugely less than LiP0). Fire? Yes, fire is a MAJOR consideration with any lithium chemistry pack and LiFePO4 cells are a LOT safer in that regard, followed by LiIon, and LiPo last of all (most dangerous).
Tesla? LiIon cells. Tesla fires? In the news for being hard to put out. Bear this in mind. And I'm not picking on Tesla because Hyundai, Chevrolet, and recently Ford are all on record at some point or another warning against parking within your garage due to there being a risk of fire. Think your RV is immune? Think again!
Note 2 - think carefully about the house chemistry. The OP has posited using LiFePO4 batteries, and I congratulate them for it. I would use the same approach with the principal difference being I'd rather four 100A batteries than each 400A battery. Yes, means 12X 100A batteries instead of 3X 400A units - but this is carpentry versus architecture.
Maybe my view will be viewed as quaint or archaic so maybe I'm wrong or lacking in data, but I'd rather deal with one of my 100A packs going south on me than the equivalent of four packs going south on me at once (I use the term battery and pack interchangeably as they're both made up of individual cells).
Speaking of which, and FWIW, if you open any one of these 100-400A 12V battery packs, you'll see they're actually made more like a Tesla-pack, e.g. comprised internally of a butt load of individual 18650 cells. As an aside, this also means you can go in and replace a defective cell (or ten) and bring the entire pack of 100 cells, or whatever, back to life. In theory. And you do know those packs (Ford, Tesla, Chevrolet, all of them) are water cooled, right? THINK!
This brings us to voltage . . . typical 400W panels are 42V, making them great for dealing with 36V systems. Three 12V packs (batteries) in series become 36V, or in parallel remain 12V. If it were me I'd rather deal with moving 36V around as the wire gauge is reduced compared to flowing the current at 12V. Just saying.
Note 3 - regard wiring and sizing. Dealing with DC amps and wire gauge is tricky. I'd advise buying an infrared temperature gun. Like the ones hospitals used at the beginning of the pandemic when they took your temperature aiming at your forehead. What for? Check the temperature of the wire you've installed when loaded. Basically, heat is bad juju and a great indicator you're too light in the gauge department. Use your judgement by accounting for how long a load will be in place.
Finally, I am nobody to give advice on consumption, but it strikes me the advice of using Watt-meter is solid. And these things are available in more configurations than the Kill-A-Watt device mentioned.
This one is good to 180A and will prove a useful tool. Using it is easy but practice can be tricky because the question is, what connector do I use? Sadly, there is no one standard.
Note 4 - on my business-website we sell three convenient to use connectors rated at
30A,
60A, and
90A (DC amps, totally different from AC amps). These connectors are, however, widely available so I am 'not' shilling them to you guys as they're merely an accessory, meaning not what we 'do'.
Anyway, these types of connectors are a handy way to establish 'your' standard for testing and interconnecting some devices. And maybe not obvious, but anything flowing more than 90A of current will need something else. FWIW, this same brand makes one available to 150A, it's just that we don't handle the larger ones preferring to opt for a
bare 5.5mm bullet connector instead because the plastic housing for the 150A is bulky and thus, somewhat incompatible within the space constraints of model airplanes. Anyway, the point is you should establish 'some' interconnect standard and then begin testing some of these things.
Earlier I mentioned fire risk so allow me to bring up fire, e.g fire on purpose (and yes, I do this a little bit tongue in cheek). Why? It's because 'I' prefer cooking on fire and thus, a gas eye makes more sense to 'me' because it removes a huge resistive load from DC-power consideration. To which I will add; an instant-on gas-powered water heater is compact and adds another approach to the luxury of hot water. One that will greatly reduce electric current demands on your system. But, of course, everybody has their own take on perfection.
What I'm saying is, pick and choose your battles because an all-electric setup may, or may not be wise. As always, it depends.
