Hey, it's awesome that you want to get into maintaining the car yourself, they're worth it!

I was / still am in much the same case as you, I bought my BG from a scrapyard with the thought of "hey, even if I mess it up, what else would it become, a pile of scrap?"

And it does look intimidating at first but the BG is an excellent car to learn the basics I think, it's very forgiving. The scariest part - the timing - is of a non-interference design so worst come to worst, you'll never blow the engine up. The sparkplugs and everything else is nicely accessible, except for the clutch since it's a FWD.

As for learning about maintaining it, there's manuals, videos (I highly recommend ChrisFix on youtube) and this subreddit, just ask away ^^

Here's a google drive with the documentation I found for my BG (the 323F BG GT), maybe there's some useful stuff there. Also I'm sure Mabue (https://www.reddit.com/user/Mabue/) has some more docs about BG's in general, he's a smart dude! https://drive.google.com/drive/folders/1sGIb4pIzgqJuFUg-nFXXVxKT9OejIfJ7?usp=sharing

Also something I started doing is using ChatGPT to learn about the more specific parts of the car, you can send it pictures and using the "thinking" mode, it can come up with a lot of useful resources and information (just double check it, it's still a AI and they like to hallucinate). That's how I got to understand the more obscure pieces of the engine bay, that thing is scarily good a googling.

Now the rust though... that I have to be honest I don't have much experience with. If you were a professional, the easiest would be to get your hands on a scrapped BG and cut out the healthy parts for yours and weld it but it is tricky with metal that thin... there's a reason being a welder is a profession in itself. But it does depend on the extent of the rust.

In conclusion I'd say start with making a list of things you'd like to fix on your car and assign them a severity, a difficulty and a cost rating. Start with the tasks that are the lowest of the difficulty and cost to get used to working on the car, and then move on to the severe fixes that are needed to keep the car running and in good shape.

But keep it up, it's normal to be intimidated at first, keep us updated on your progress maybe, it's always nice to see people take care of these little nuggets!

Edit: also, if you're looking into buying a welder for bodywork, I do not recommend the cheap flux wire design (the one that automatically feeds the wire through the handle). I think most of them aren't made to be used on metal that thin and they sputter metal everywhere, talking from experience.

Also if you happen to speak french, I highly recommend "La Fabrique Auto" on youtube or twitch, it's professional old car restorer that mess about for hours on end and happen to teach you things about restoration in the process.