Re: legal motorhome capacity
You will need a passenger endorsement. What you need beyond that I'm unsure of. In Minnesota you would also need your Class B if you register it for more than 26,000 lbs which you may have to do. 20 people * 150 lbs each=3000 lbs right there. My 65 passenger bus weighs 18,000 lbs empty without fuel. You will also most likely need an air brake endorsement if your bus has them. On top of that then I would find out specifically what your state DOT requires in terms of inspections and such.
It might be cheaper and easier just to have the rest of the crew in a van following the bus...