I think I know the answer to this, but just to make sure. I have painted my car in pieces, with bc/cc. As I finish each part, I have sanded it down to smooth 1500. Now I intend to assemble the car, but it will take me a few months. Can I buff and polish it then?

Sure, the only difference it will make is the surface will be harder to buff since it will probably be fully cured. In some ways that is not such a bad thing since it decreases the chance of burn through. Just don't forget, you still need to tape your edges before compounding and buffing. Glad to hear you're reassembling those parts before you do your buffer work. Accidentaly slinging a newly painted part across the room can make a grown man cry.

Why do I need to tape off the edges before compounding and buffing? I've never buffed before, except for my test panels, but I didn't come close to any edges.

You stand a chance of burning thru.

trust me its not very hard to burn through on a corner, ( i've done it a few times)

NO ITS NOT. I did it too. About 1 hit with a wool pad and it seems like you just hit it with a grinder.