C owner here. For what you want to do, live in it for a cross country trip and occasionally sleep four, I would lean toward a small C. For fuel mileage approaching 16 MPH, this means a View/Navion, or one of the alternative Sprinter C's from Thor (FourWinds, Chateau, Dutchmen brands), Coachmen, Fleetwood (Tioga, Jamboree brands) or Gulfstream.
I would let the wife have a say about what the bathroom needs to be like, where you usually sleep, and how well the kitchen works for her. Not that there are many floorplan choices for the early View/Navion, but her wants could very well rule out a B (van conversion) or Rialta. Letting the wife have her say about the house was the key to getting her assent to the whole RVing thing, a factor not to be ignored if looking at the longer term. The RV I would choose for myself would be very different from the one chosen for the two of us.
Tom Test
Itasca Spirit 29B