Down here in Georgia, I was initially told that I'd need to get a class B CDL with school bus certification regardless, but then the lady paused, asked if she could have my name and GA driver's license number and call me back after a few more people got in (I called as soon as the dept. of driver services opened). She called back an hour later and said, "It's obvious that you don't intend to use the bus commercially, so everyone here agreed that you do NOT need a CDL. Drive safe and enjoy your RV!"
Now, getting a bus registered as an RV might be a little trickier. The county folks are very nice and said that I just need to call the state dmv to get the title changed (it will require an inspection that they can't do at the county level) and then re-register; the state dmv were much less patient and told me that they don't change the title, once a bus always a bus. (I know this is not true, because I have seen a few buses locally on Craigslist that ARE titled as RVs, so obviously SOMEONE has done it.) Since I don't actually own a bus yet, I didn't press the issue, but it does seem like it's going to be a bit of a headache if I do it down here.