I’ve been doing my own builds and maintenance for a few years now. Easy really when you know what to do.
I now work / volunteer at a bike recycling charity.
I’d suggest that rather than soak up YouTube videos and Park Tools blue book, search out a bike maintenance or build course. ( I’m not against videos, we all use them !! )We do both (I’m in the UK) and although you won’t suddenly have all the ability and know how to use every tool, you will have had a good introduction to which bits go where and how to best put them together.
When you’re ready, you’ll need some tools. Generally I’d recommend spending cash on tools you will need to use a lot. Allen (hex) keys, screwdrivers, Torx and similar, get good ones. Special tools like cable cutters are definitely on your list. Other tools will depend a little on the brand of kit you choose to build ( cranks, bottom bracket etc ). Oh, and workstand - I could tell you why a 200£$E one is a good buy, but tbh, a 40£$E will be just as good. My home one only cost me £25…
It’s up to you as to whether to do a new or used build. Both have their good points, but I would err on building a pub bike or two before building your Sunday best steed. Don’t start on wheels as you can mess things up big time - though there is less black magic than people may lead you to believe. It’s patience mostly.
Good thing about building your own bike, is that you know it all works, and how to fix it. You’ll learn al lot, and have a great deal of fun too.
Enjoy 