First, consider do you want to pull a large trailer? A 5th wheel would probably be your best bet, but you will need a large truck. Do you want to use that large truck for your everyday trips, like running to the store? I don't. I have a class C and tow a small car. Second, be aware that any RV will "shrink" the more you use it. What looks big at first will become cramped and confining,especially as your family grows. In real estate, the saying is "location, location, location". In an RV, it's "floorplan, floorplan, floorplan." There are a lot of bunkhouse models on the market, take a look at them. It sounds like your family has an exciting life ahead.