We are going through the same thing in Pa, catering/vending. I contacted the dept. of agriculure in Montoursville (lycoming county) not sure where you are at. But we were told we don't need a commercial kitchen to use since we do all our prep and cook everything on the trailer. We do have a 3 bay sink for wash/rinse/ and sanitize, plus a seperate sink for hand washing. Hot and Cold running water. Enough water on board for an entire day. We have a coulpe small catering jobs under our belt, and plan on being setup in our front yard for roadside pick up for home penn state games. (our property is zoned commercial) There are 2 different licenses you'll need,one for catering and one for vending. Its a ton of paper work and seems like over kill,, but that's the government for ya.. Anything I can help ya with just ask, you can e-mail me if you want email@example.com
We don't have it all worked out yet, but working on it.. Good luck.
ps. serve safe is a must, but it isn't hard, just a long day..lol..