Want to fix an old bike

I've been thinking lately that it would be an interesting hobby to get an old bike and work on it. Unfortunately, I'm faced with two difficulties:

1. Lack of mechanical knowledge. I have installed a fender eliminator kit, but never done any other work on a bike. It was really easy, but I can't imagine anything else I'd need to do being that easy. I'm reasonably good at figuring things out and solving problems, and was thinking of basically relying on youtube/forums as my source of instruction.

2. Lack of space/tools. I live in an apartment, but have garage space in the basement where I park my bike. There is enough space for a second one. I also have the standard tools everyone has to: wrenches, socket wrenches, pliers, hammers, electric screwdriver, etc.

My plan was to buy an older (70s-80s) Japanese bike in marginal working condition and rehabilitate it. I've always wanted to do this, but have never been in a position where it seemed feasible. I was inspired because my neighbor was working on his and it occurred to me that apartment living might not be a total barrier.

Any advice before I get started for what I will need or what kind of bike I should look for, or advice in general?