There's a lot to know about polishing metal, but suffice to say you would use a "sisal buff" with either a black or brown rouge to "cut" (ie smooth) and a cotton buff with a blue or white rouge. My recommendation for the minimal amount of equipment to do the most types of things is a sisal with brown and a cotton with blue. Brown seems generally safe for all metals (whereas black isn't) and blue is a safe finish for both metals and plastics.
I'm by no means an expert, but I've recently gone through what you're going through. I ended up with the HF 6" buffer with various wheels and rouges. But learned quickly that it doesn't need to be as complicated as many will make it sound for our pinball parts. If you're trying to restore a vintage car to a pure mirror shine, then yeah, but getting some pinball parts sparkling clean isn't all that complicated.
