Legal Question in Construction Law in California

That's a local ordinance issue on the basic permits. Check with your city and county governments. You probably also have CalOSHA, EPA and other environmental and occupational health issues to deal with. This is not something you're going to get covered properly in a free question/answer website.

Just as a related thought, though, when I was a teen in the 70's, my neighbor used to restore old cars for a living, in his garage. He did the most BEAUTIFUL 12 coat lacquer finishes, hand sanding between coats, and rubbing out by hand for hours, until he had surfaces that looked so liquid you thought they'd run off the car, and so deep you thought you could dive into them. Fortunately or unfortunately he'd be out of business now with all the regulations involved, and really quite frankly, I hope the people who live there now aren't eating vegetables grown in the yard, if you get my drift. Bottom line: those days are gone. Probably best to find a commercial site and follow the rules.

I'd predict you would never be able to obtain the permits for a conventional garage in a residential area of Hayward. The air quality management people would require specially-constructed this-and-that, including a vapor recovery system.