As others have said, speaking as an electronic engineer, solve the power issue first. And I don't mean estimate or take a guess, I mean go and talk to someone who's already done it professionally. Don't take a single step further until you have that solved. As even if you could get a generator big and quiet enough, the existing power system may not support the loads you would be asking it to and you may need to rewire it. The cost could be substantial and I doubt you want to go through a complete set up each and every time you have a client.
I've worked on ambulances and they have no where near the power draw required for what you want to achieve. Most of the systems are battery powered first and the simply charge off the alternator, there is no heavy load for sustained periods of time as you will require here.