Don't worry over building a lower, it's really easy. It's building an upper that if you're inexperienced should be avoided since that's the part of the gun subject to the high pressures and stress of a round firing. As for the stock, I must respectfully disagree with Mongo. I have an Ace SOCOM and it's a great stock. Solid, adjustable, and the foam sleave over the tube is pretty cool too. This thing I swear could take down a door and not bend. Granted, an ARFX isn't as tough, it's still a very good stock that you can pick up for under $100, buffer and spring included (I can't remember if you need a tube or not). On the other hand, you can pick up a good quality plastic stock for about half that, but if you have the $$, go with the Ace.
FYI, unless Adco has them in stock, don't expect anything special ordered to come in from RRA for the next long while.