[rick3000]

I agree with DJ.
It sounds like a great idea. But I would avoid doing anything to big. Think about the car care you have done on your cars since the '80's how many times have you messed up and had to replace a part?
I know I've messed up a few parts on my cars that have had to be replaced. The last think you want is someone's $60k+ P-Car getting damaged, and you have to pay out of pocket. Especially, since some parts cannot be bought from a parts desk.
One example of this I know of, are speaker grills that are painted to match the cars interior. The parts desk only sells black, so if you do a speaker swap for someone and mess up there painted grills your (insert profanity here).
It just depends on the kind of stuff your talking about doing. But it sounds like a great idea, if you stick to what you know and don't do anything that would inflict a large liability.

What type of stuff are you think about doing, strictly maintenance/car care or upgrading/modifying/etc.?

Also, the legal stuff goes as far as you want to take it. If your just doing stuff for local owners you know you'll be fine in your garage, taking cash. If your advertising, and getting random people, look at getting yourself incorporated for liability reasons, but that can cost some $$$, plus yearly fees.