Unless you have enough bucks to start your own bank, going commercial isn't an option. Cost would be in the thousands anually.
Very likely you won't be able to insure the coach for comprehensive coverage. You 'friends' may want to consider some sort of personal insurance on valuable instruments, 'fex and sound equipment. Leave the bus unattended at rock music festivals and I'll garuntee your $#!+ will be stolen.
Liability only is probably what you'll end up with.
No special license is required to operate a 'motorhome'...but, technically, the minute you move your band members from one paying gig to another, the bus is...technically...in commercial operation. Not sure that the insurance agent really wants to know what you're doing. As when registering the bus, don't volunteer any info. Don't use the word 'bus'...use camper, or RV, or motorhome...or POS...anything but 'bus.' The agent is responsible for asking the correct questions...you're not an insurance expert...? Neither do you want to overtly misrepresent facts. That'll get your insurance voided if you make a claim. You're obliged to accurately (if limited) answer insurance and registration questions.
You may be required to prove that the 'RV' has certain RV appointments before the state will alter the reg to motorhome status. Be prepared if that comes up. Don't balk...just get busy and find some cheap RV conversion components and install.
Plan on buying a service manual for the bus, powerplant, and genset. keep in with you when traveling.
Don't count on the fuel guage until you're familiar with the accuracy of said guage.
The bus, if it doesn't have an auxilliary fuel tank (big box in the front bay), holds about 120 gallons of useable fuel.
NEVER run out of fuel. I'd keep that sucker at least half full all the time.
Running out of fuel in a car is a PITA. Running out of fuel in an MC9 is a major PITA.
Hope you of you guys is a mechanic! Working on that bus will add to your ability to create screams for your 'metal' art...
If y'all have never driven a bus or truck, that's another subject. Just getting the park brake off requires prior knowledge.
Be very careful with your new toy. You'l quickly get acclimated, but the opportunity for castastrophe is high early on.
Always keep up with RH turns in tight areas.
Good luck dudes, JR