get both belts as they're not too expensive and you might as well do them both while you're at it. any parts places should be able to give you the right ones. you may also need to replace the belt tensioner pulleys too if they haven't been changed before. otherwise, you may get squeaking noises with the new belts...
Yeah, I went and bought the belts, and turns out the tensioner pulleys were the problem. Bad bearing in one of them. Also discovered that the radiator is leaking ("coolant leak somewhere" in dealership lingo). Autozone quoted me a new radiator, and gave some tips on how to change it as well. Likely a 2 hour job.
I am also interested in the brakes situation. My FX isn't tuned up or anything, but I have 22" lexani's and rusty pads/calipers etc is not sexy.