You will be hard pressed to fit a queen size bed in a mid-size bus with handycap door, unless you find one with the door up-front just behind the stair-step door. Even then, you will need to block the rear-door. With a rear-engine (usually found in only full-size buses), the bed goes right on top of the motor compartment, so no problem.
Dog-nose is your choice. It will give you more ground-clearance compared to a flat-nose transit-style bus, like I have. Still, I think I have more clearance than most RVs. Don't let anyone tell you dog-nose is easier to work on. I work on my Cummings in my BlueBird, out of the sun, rain, and wind!, with no problems, no ladder needed. Reminds me of my old 1977 Dodge van; not a Ford or Chevy van: they are a pain to work on. Replace the motor? I don't need a huge a-frame motor-hoist, nor a lift, it seems. The bumper and front grill come off quick, and the entire motor and tranny combo could be on rolling floor jacks and rolled out the front from under the bus without too much hassle, so it looks, since the front axle is behind all of that and not in the way...
But in the end, we can only advise you on things that are important to us. You just need to look, and look, and look some more. I like my BlueBird, and I think it is a solid, quality construction, that is easy to fix, although the wiring reminds me of an old 1970s AMC Jeep, and looks like a pot of spaghetti, and they don't want to give me a wiring diagram beyond the motor. As a mechanic for 20+ years, I see plenty of vehicles that don't get a good review from me on any of these points, but I haven't looked at many different makes of buses from a mechanic's point of view.