1982 XS 400 Maxim, running now.

Earlier this year I decided I wanted to learn how to ride a motorcycle and learn to repair a small engine, I asked a family member to help me and we ended up picking up this lovely little bike being sold for parts, it had a smashed instrument cluster, a carb that was full gunk, rotted vacuum lines and had been left to sit for a few years. After a few weeks it's running like a beast, I'm loving it and can see why there's a forum dedicated to them. I was hoping you guys might be able to advise me on some QOL changes I could make or spare parts I should buy for the things that are gonna probably break or wear out eventually.

How is the fusebox? Most of them need replacement at some point.

Typical maintenance stuff:

Check under sprocket cover for leaks. Replace seals as necessary.
Check the chain. Replacement chains are cheap, broken chains can wreck your bike or make you crash.
Check your bearings. Even cheaper than the chain, and also cheap insurance. Buy name brand, five dollar ones on eBay aren't worth it.
Check your brakes. If the hose is original, ditch it. Old rubber can surprise you in bad ways. Plus you probably need new fluid.
Check how old your tires are. https://www.utires.com/articles/read-date-code-motorcycle-tires/ Again. Old rubber can surprise you.

Beyond that, they are pretty trouble-free.

Improvements...

Depends on what bothers you personally. Me, I tend to upgrade headlights. Bulbs just weren't great 40 years ago.

Otherwise... Ride the hell out of it. They are fun.

Thanks for the response, I forgot my password and couldn't login for a bit but I appreciate the help.
I've worked on several things and it's a semi reliable bike. I think it might be a good commuter eventually, it certainly is a very good learning experience.

I can certainly recommend tc bros brake hoses. http://www.xs400.com/threads/tc-bros-brake-hoses.20896/
I never realized how spongey my brakes were until fitting them. Though even new rubber hoses would feel better than 45 year old ones.