I bought a couple and I've already had to do a lot of work.
It turns out, it's not that difficult. The systems are simple, each on their own, with few exceptions. When you isolate systems, you can just learn one at a time without pressure to be a whole mechanic. I still reserve the right to send it to the shop if needed.
I haven't had to rebuild an engine yet, but I've been all around the wheels, tires, axels, AC, fuel system, timing, vacuum lines, trailer wiring, brakes, coolant system, and of course I service all my own fluids.
I put it off way too long. My advice is to start now, if you think you'll like it. And you can start with mowers...a whole lot of the tools and concepts transfer.
(Owner of two old german cars, one which has seen a partial engine rebuild, the other significant chassis welding. No formal training doing either.)
Find an older VW (or similar) and that's the basics and a bit more. Definitely replace the fuel lines on an old VW, but otherwise drive it and let it tell you what needs doing. IMHO, fuel injection is nicer than carburetion, but you some early injection systems have a bad reputation; Bosch L-jetronic seems pretty reasonable. Some people really like carbs though, so up to you.
Lots and lots of forums, some of them helpful even.
When it's an extra car that you have for fun, you don't have as much of the 'needs to work asap' stress and you can also get one that's more questionable cosmetically to save some money.