I buil my J&T LW Tactical kit on a RRA lower:
It went together perfectly, functions perfectly (so far), and the color match is great!
As for your other questions, help everyone out by defining what you consider to be "accurate". 1/2 MOA at 100yds? 1MOA? 2MOA? What kind of shooting are you doing -- plinking, match, hunting?
#1 & 4...I don't know so I'll defer.
#2 RRA and Armalite make nice 2 stage triggers...don't know about others. Some forms of competition require the use of 2 stage. If it's not required, you can save the $ and make a nice single stage trigger pull...search the AR forum on how to do this.
#3 I'm not sure on advantages of 1 over the other, but I *think* mil spec is not chrome or TiN.
#5 If you get a standard flat top, you can get adapters to go higher if needed.
#6 Mine came with a brake. It's nice...but not needed. But IIRC, a brake will preclude the use of a free-float tube...or at least, you'd never be able to remove it. You'd have to get rid of the brake to remove the sight tower/gas block, to remove the FFT.
#7 For all but high level competition, I doubt it.
#8 Picatanny rail is like a Weaver style attachment rail...lets you put quick detach accesories wherever the rail is.
#1 For civilian guns, the bbl profile is the only difference that I know of.
#2 It's a mock M4 because the the military M4 has something like 11-12" of bbl, and 5" or so of supressor. The civilian versions can't do that because of the law.
Hope that helped...and hope I got my facts straight. If not, I'm sure I'll be corrected.