I've got a few friends who rent out campers. They all say if you use your own bus a lot don't rent it as people inevitably want it when you do. Insurance seems quite high to but then I guess the customer pays it anyway. As for numbers of vehicles I have friends who rent 1 no issues but seems best to have 2.
I seem to recall a feature in the vw bus mag in jellybean campers. They only rent the one van. Maybe in here, not sure.