I'm also fairly early in the conversion process but here are a few things I've learned:
Neighbors and the local government can be a problem - Check with your home owners association and city hall before bringing a big, yellow school bus home. Several bus owners on this forum have had to move their busses off their property because of zoning or HOA issues. I had to extend my driveway in order to legally park my shuttle bus at home.
Insurance can be difficult to find - Most conventional carriers (allstate, progressive, gieco, etc.) won't insure a bus conversion at all. GMAC is the go-to insurance company for bus conversions but they'll usually only give you liability coverage. GMAC liability-only insurance for my E-450 based shuttle bus is $230/6 months. Full coverage wasn't an option.
Repairs are expensive - These are heavy duty vehicles and parts can be expensive and difficult to find. Most schoolies and shuttle busses that come on the market are being sold because they have exceeded some arbitrary service life (either in years or miles driven) or because they are in need of lots of repairs. However, if you shop carefully you can find good, low-to-medium mileage vehicles but budget for repairs. Diesels, in particular take A LOT of oil, coolant and trans fluid; often triple what a passenger car takes, and the vehicle you get will likely need a good going over right away. The cost of 6 big tires and a brake job will make your eyes pop. If you can do the repairs and maintenance yourself the cost goes way down but the price is still considerable.
Everything takes way longer than you imagine - Seems like everything I want to do requires three trips to the parts store or home center. Parts need to be ordered. Rain, snow and heat will slow you down. Family stuff intrudes. Motivation comes and goes. Make your best estimate then double it.
Everything is more expensive than you planned - It's fairly easy to estimate the big stuff, but the little stuff (fasteners, adhesive, insulation, lumber) really adds up. I say again, make your best estimate then double it.
Towing can be a problem - Big vehicles need big tow trucks. AAA and Good Sam both have RV towing programs that are generally well rated. If you're going to be traveling a lot, calling an 800 number is way easier than trying to find the nearest tow truck out in BFE.
With all that said, if you step into the schoolie world with your eyes open it can be very rewarding. You're taking the proverbial sows ear and making it into a silk purse. That, to me, is very attractive. You'll also never have the feeling there's nothing to do.