Anyone over 18 can sign the wavier, under that of course get ur mommies to sign it. You get to choose your deductible be it $500 or $1000 or whatever. The higher your deductible, the lower your premiums will be.
Anyone driving the bus with permission is covered underneith your policy. Lets say you allow Echo to drive the bus, and he superwave dashes into a nearby mountain, your (jupiters) auto policy would cover the vehicle. BUT if Echo has full coverage on his own policy, you can claim it underneith his own policy, thus leaving yours (jupiters) policy unaffected.
How much premium are you paying for the bus? With what company? How much liability limit do you have? For a bus i would get 250/500 Bi limites with 250 in property damage.
In case you haven't noticed, im an insurance agent =)
Questions? Feel free.