Man, I started the same way. Bought an RRA lower for a good price one friday night at home, looking at gunbroker with too many beers in me. Next I started perusing the EE section, and a few months later (I wasn't in a hurry) I found a complete upper, which was just what I wanted.
Now I've finally bought buttstock parts and will have my Lower parts kit soon. ( I got busy and waited to ship my lower - now I'm getting the LPK from the same guy shipped for nothing.)
The guys on Equipment exchange are great - you can get new parts from dealers ( Got a very pretty 4 pos collapsible from Tic) or good deals on used stuff. Take your time and don't jump on the first thing you see - check out the picture threads - there are guys here who own more ARs than I own guns, and some of them cost more than my whole collection! Figure out what you really like, and start collecting parts. Just read a lot. Lots of experience here to draw on. I could have bought a cheap kit from one of the many who sell them, but I wanted an A1 upper, and ended up with some really nice parts for just a little more. I figure quality is worth it. You don't have to spend an arm and a leg building an AR, but you sure can! Take it one step at a time. I've spent 6 months collecting parts and will finally have a rifle I can shoot by the end of the month. Just my .02
BTW - that was a pretty cool present from your friend. Better than a watch!