The smallest F53 (class A) chassis is 16,000 lb GVWR and 158" wheelbase, so suitable for a class A of roughly 25 ft. However, very few class A are built that short. Maybe a Winnebago Intent at 26 ft. Most everything else in that size range will be a Class C and most likely on the Ford E450 chassis (14,050 lb GVWR). The E450 is a good match for a coach of 24-29 ft, but lengths of 30-31 ft will tax it rather heavily.
The necessary size for two travelers on an extended journey is very much a personal thing, but I recommend you err on the side of extra space. And consider towing a car for local sightseeing if you worry about city driving in a 25-28 ft vehicle.