Would you be willing to buy your customer a new replacement Camera if you screwed up your repair? Legally you might have no choice. Practically, your business name would suffer if you did not.
Speaking from experience, I had to replace a $900 circuit board when my micro-tip soldering iron overheated a board lead junction, and I had a college degree in Electronic Engineering! All profit from 10 previous repairs went out the window. Serious Electronic micro-circuitry courses are recommended for today’s cameras. Then there’s your electronic tools, and analyzers; not cheap.

I've been repairing camera equipment for over 30 years now and, while you won't get rich doing so, it does pay the bills. It's also very complicated. You need to be comfortable working with micro electronics and miniaturized mechanical parts. The initial investment in test equipment and specialized tools is steep and then there's the cost of learning how to use them. When I first got into camera repair there was a college course with a degree in photographic equipment technology as well as a National Camera course but those days are long gone and it will probably be a trial and error process to learn what you need to know. That gets expensive too.

Don’t even think about it. You wanna do it as a hobby, fine; but as a business it’ll be no joy. Cameras are very delicate. I’ve tried my hand at repairing lenses and learned good lessons. For both, lenses and camera bodies it takes a very steady hand, some experience, and a good selection of special tools and calibration gear. That already means a significant investment before you even start. Also, as some readers have already mentioned, getting parts in a timely fashion might be difficult.
I’ve been fortunately able to find a local fellow with years of experience in lens/camera repair who also happens to have a thriving sales/exchange establishment. Works out of a large converted detached garage that could easily be the envy of any regular photo shop. Fun place to visit and browse (got a great deal on a like-new Canon 85mm/f1.8).
May not mean much but I just wanted to share my thoughts with you. I love this website.
Cheers!