My bus is a 1967 Ford Superior 47 passenger set up the same as you're thinking. I think it is only about 28 feet long. It has 7 rows of windows. I don't know how wide it is, but a full size motocross bike will just fit sideways. I think they take 8 ft. I have about 3 windows worth of bus that is garage, giving me enough room for two full size bikes, maybe a third. If I had a wider door in back I could problably fit 4 bikes, the limiting factor is being able to get them turned sideways.
It sounds like you will need a much bigger bus to have enough room, if the camper/hauler space is going to be that large and separate. Don't forget the hood, stairs and driver's seat being part of overall length.
This is mine.