The chainring bolt will be easy to find. Just drop by your local bike shop and they should have what you need. No need to replace all of them unless you're obsessive about them matching perfectly. While you're there, I'd suggest picking up new cables and housing, tires, and brake pads. If you're going to tear it down for a good cleaning and overhaul, you might as well put it back together with stuff that's going to work smoothly.

Have fun with your "new" bike!