You want to pull a heavy trailer? You want to have easy maintenance? You want to be able to have the motorhome worked on anywhere? Get a truck conversion on a Freightliner, Kenworth or Peterbilt. You'll be much happier with it. Buses are a big pain in the butt.
Have you been to see any buses yet? Which ones have you actually been inside / driven / ridden in? It will make a huge difference to put your hands on a bus and see things in person. Given the trailer you want to pull, there are a few winners and a few losers (at least on paper) but none of that matters till you start to see things up close.
Just buy a conventional motor home and get it repaired anywhere, eliminate a lot of future drama, get insurance much easier, get better fuel mileage, as long as you stay away from Ford gas engine, avoid having your savings drained due to a breakdown out on the road, and enjoy traveling more without constant repairs. Oh, and save money every time you change the oil.
Look at Beaver,Foretravel,Vogue or Country Coache in the 35 to 38 ft range they will have a Cummins or Cat power train and are built strong