I sold everything you listed here except a sub for $500 about a year ago. These speakers are great, and the p362/p363 go on sale at Fry's for ~$300/pair quite often. The rest of the speakers, are cheap and you could probably get a new set for about the same. I would recommend waiting for a sale at Frys before spending $850 on used speakers.
I think if those speakers are in good shape then that is a very good deal. The Infinity sub isn't the best around but it isn't bad either. I would go for that set with the intention of upgrading the sub later, to something that can really dig deep, like a Hsu, Outlaw, or Rythmik.
I think the differences b/w 362 and 363 are just cosmetic. In fact, if you open up the p363 cabs and look at the crossover, you'll see p360 marked on it. So its safe to assume that the cross overs are the same, and by that extension, the drivers are also the same. If you get a good deal on the older p362, go for it.
The guy says he has no way of powering them since he already sold the receiver and they have been in storage for the last 2 years.
Would the BIC PL200 be an upgrade? Or anything in the $200 range?
I don't think that PL200 would be an upgrade from the Infinity sub. You would have to go to the larger $600 subs from ID brands, like Hsu, Outlaw, and Rythmik before you get a substantial increase in performance.