I'm a relative newby myself. All I can really say is listen to Tom.

I'm also a HUGE fan of RRA, and I'll echo his comments that you're better off buying a complete rifle. You'll hear it over and over and over again -- the guns that fail the most are the "Frankenguns" of different upper / lower or things that people put together themselves.

If you do decide on the 16", definitely go with a mid-length gas system.

18" barrels with a rifle-length gas-system are the ****. I know CMMG offers some. Not sure of anyone else does (short of custom).

I really, really hate the M4 adjustable stock. Really.

The Magpul is nice, but its heavy. I've read good things about the Sully stock. I've got an A1 (Cavalry Arms) and a couple A2's (Armalite). I like them.

Mike