Definitely steer clear of that Stoner. Way too many reports of bolt lugs shearing off after a few hundred rounds.
As far as the FA carrier, that's a good thing. It will work in any standard AR.
No need for external plating, in fact it's wise to skip it and look at specs instead. If you want the best specs look at BCM's standard BCG.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together. You'll remember the quality of a gun long after you forget how much you paid for it.
US Army 1966-69, VFW Life Member, Retired Geek