OK, a couple of comments.

First off, you may be the beginner, but, trust me, nobody here is essentially smarter than you are. The advantage any of us have is experience. There's no need to apologise for not knowing the answers and therefore having to ask the questions. Every one of us were in your position at one time or another.

OK, on to the specifics. You're dealing with a late 80's bicycle which is going to make parts hunting a lot easier than if you'd have gotten something 15 years older. First off, by this point English threading, both in the bottom bracket and headset have taken over. Assuming you have a built-in rear derailleur mount on your right drop out, it's standardized, too. There's no dealing with odd French, Italian or Swiss threadings. However, just in case I'm mistaken, French and Italian threaded parts are readily available.

Parts for vintage bicycles are easy to find. First off, there's eBay - a virtual treasure trove of whatever you could possibly need. If anything, it's such a plethora of riches that you're probably going to find yourself overwhelmed in short order. If that doesn't work, find a local bike shop (LBS in this group's shorthand) that still remembers the older bikes. That kind of local resource is worth it's weight in gold, assuming you can find one. Secondly, at your bike's (relatively) recent vintage, you're not limited to vintage parts unless it's important to you to keep it within the time frame from which it was originally built. If you're just looking for a rider - period - current derailleurs, cranksets, brakes, etc. will work just fine on your machine.

The biggest stumbling point you might find is if you've got indexed shifting on the rear derailleur, the kind where one click of the shift lever means changing one gear. If you've got that, you may have to pick your components a bit more carefully, just to make sure they work together properly. It's not that big a deal. If however, you've got shift levers that don't click, work on friction, and you do slight adjustments to the lever after snapping into the new gear, the sky's the limit. You could make a 1940's Simplex rear derailleur work on that bike with no problem (assuming you'd want to).

New brake pads, especially Kool Stops, work BETTER than the old stuff. I've just changed over to said pads on a Weinmann centerpull equipped Raleigh that I own, and I never knew that Weinmann brakes could stop so well.

My best advice is to learn what was state of the art in 1989, use that as the baseline for replacement parts for your bike. As you learn more, you'll find out what works well, what works OK, and what barely works with your current setup, and make your plans accordingly. At the very least, make note of what the bike currently has, front and rear derailleur, crankset, shift levers, brakes, brake levers. Plan on replacing with the exact item if something breaks in the immediate future. Then learn the alternatives.

Assuming the bike is in good running condition, and you're taking reasonable care of it, I can't see why you'd need to replace anything other than tyres and tubes in the near future - unless you're looking for a significant performance change (upgrade?) in some certain area.

I've been doing vintage cars, motorcycles and bicycles since the late 1960's. Of the three, bicycles is far and away the easiest - both in terms of mechanical complexity and parts availability.

Syke
Deranged Few M/C

Parts which are most likely to fail include aluminum cranks, rims, handlebar stems, and handlebars. That's why most of my stems, rims, cranks, and bars are significantly newer than my frames. I tolerate a few anachronisms in the interest of personal safety.

I have had three frames fail, never causing injury, and always permtting me to "limp" home gently. I have had three left cranks fail, one time causing a fall, the other two times harmlessly. I have had one hub flange crack, again inocuously.

Depends on where you live. Some cities have good shops or access to used parts. You can also ask here in forums if anybody knows where a specific part can be found.