It was inevitable I miss a few categories.......
No disrespect meant, just pointing out that it's a valuable skill few take the time to learn properly.
It's surprising that people still think that working on automatic transmissions is some sort of black art. 727s and 904s are really simple. If you can build an engine or a differential you can build a Torqueflite. Sure it requires a few specific tools but for the most part it’s a pretty straightforward proposition. Racers do it in the pits.
And like transmissions, painting is not hard in and of itself. Yes, it also requires some specialized tools and equipment but beyond a compressor, it’s not a huge investment. Successful paint is all in the prep anyway which does not take a lot of specific skill, just elbow grease.
Taught myself how to paint last year. I re-did my trunk, engine bay and the whole undercarriage. Came out good. I didn't do the whole car but prepping and painting uneven surfaces with lots of holes and angles has to be more difficult than painting long, flat surfaces.
Definitely need an appropriate area to paint a car or even part of one. You can make a booth out of pvc pipe or wood framing and plastic sheeting. Stick an exhaust fan in one end and you're ready to paint. I didn't do that when I painted my car and I made a mess with over spray. I was smart enough to wear an appropriate cartridge respirator and face covering whenever I had a paint gun in my hand though.
All this stuff you learn by doing though. Like all learning these things get easier the more you do them. If I haven't done a particular task, I research the subject, buy what I think I need and go at it. I'm not paying anyone so beyond whatever tools I buy the only cost is my time. Can't imagine how much I would have paid out to have other people do all the stuff I've done on my car.
There's downsides to doing everything yourself though. Mistakes are on you. Things also tend to take way longer when you have to figure out how to do something you've never done before. Your time is worth something and the argument can be made that it's better to pay someone to get things done and finished correctly so you can enjoy the car, not hate it or have to re-do stuff 2-3 times. Doing everything yourself can be a slog sometimes, trust me. I've had my car for almost 12 years and it's been in pieces for eight.
I thought of one thing I'd hand off to someone else - putting in a roll bar or cage. I can weld but not well enough to entrust my own safety to it in a bad crash. Welding takes many years to master. If I did it every day for a living I'd probably give it a try but until then, that's one thing I'm happy to hand off to a pro.