For two people a class C will be comfortable if chosen to suit your travel style.
Biggest thing you may take issue with is likely to be tank sizes. If you carried 75-100 gallons of fresh and could haul out similar amounts in grey, you will generally find "C's" lacking. Most will be around 50 gal fresh, maybe up or down 10 from there, and likewise on the grey. Black is often in the 30's
Range/fuel, most newer units with Ford E-450 have 55 gallon tanks, so figure 400 miles if you are gentle, some may say a little more, some less.
If you want a washer/dryer I know the Coachmen Leprechaun311 offers that, not sure on others.
Others on here will know the generally accepted ratio but with some longer c's the rear overhang is extremely long, others seem to stretch the wheelbase more.
Happy hunting.