Ammo (brass cased Remington factory 123gr FMJ) was supposed to hit retail hard already but they pulled it back for a redesign. At $11.99 its cheaper than x39 brass ammo. Its just a waiting game as of now.
Reloading for it would be fun considering all the .308 choices. I looked into it but wanted a Dillon 650. It would have been $900-1k to get started and right now my 2br home doesn't have the space. Theres a guy putting out preformed, primed brass for the .300blk. Its BradsWarehouse.com - Custom made 300 AAC Blackout Brass
. If you go w/ the Delta barrel he might give you a price break on the brass.
Aaron @ Delta is a Disabled Vet from the 82nd in his mid 20s. He's a great guy to deal w/ and was very helpful w/ selecting my barrel.
I like the upper you have linked. My recommendation is going w/ a LW barrel attached to an A3 upper though.