To the OP rdoty, it sounds like you are the right track, especially if you are alone. We down sized from a 30' 5th wheel and jokingly say that we have everything we had in the 5th wheel but it's all in a phone booth. It helps that we are hobbits but the amount of space that you "need" depends on your physical size and your mental attitude. We live in a 1996 Roadtrek 190 Popular for 6 - 8 months each year for the last 2-1/2 years and have travelled 43,000 miles. Back in the 70's 18' was big and 24' was huge. Most B's are 20' - 22'. Our home base is Alberta and we have family in Breckenridge CO, so we are familiar with with the elevation changes and mountains. Our unit is not a power house but it handles any mountains we have been in just fine. It has 220 HP and 295 Ft.Lbs of torque at 3200 RPM. I installed a tachometer and keep it at the 3200 rpm on steep climbs, which is around 50 MPH in 3rd gear. It is a 4 speed transmission.
The ease of driving, ability to park on the street, camp in small spaces, not towing, and be home where ever you stop, to us, is the big advantage. For some it would be too confining!
Your budget($35,000 - $50,000) should get you a good 6 - 12 year old Class B in gas or diesel. Take your time and you'll find one that suits your needs. We looked for 5 months. Also small Class C's 20-22 feet have larger bath rooms/showers, a little more room, and less money, which still may work for you.
Good luck and you can PM me with any questions.