What exactly do you need in order to be a legal and official catering business (a partnership)?
Radio station for business
You need to call your county offices and ask. My neighbor wanted to do this and sadly, didn't check on it BEFORE he had his kitchen renovated. Nothing in his renovated kitchen was adequate. I don't remember all the details: he needed at least two sinks. and a dishwasher. He needed a separate refrigerator for the food he served, it couldn't be mingled with his own food. There were lots of things. You need a tax ID, and a vendor's license.
Go to the Your Harmonic Resonance Site and read about starting a business. There are a couple of links to Tax and licensing.
call your county and ask.