You have a ton of research to do still before selecting a bus. Keep asking questions.
If you plan on much over the road time, there are specific drivetrains to avoid. Consider where you can park and build an RV when considering size. Everything in it will be "a small". With a rear engine bus, you can have a nice size back bedroom, but no outside access. Having a front engine gives you rear storage and access. You need to think about all the little things like this.