Re: First AR Build
I wouldn't sweat the lower. Mil spec with a good trigger group is all you need there. Your upper is where 90% of your FTFs will occur. Again, mil spec is the most reliable, but you can do better (but it'll cost ya). I'd find the best deal you can on something 5.56 and true mil spec, then keep it simple. The more fancy crap you add on to it, the better your chance of failure. Just my 2 cents, but it always worked for me.
I like things that go "bang"... I love things that go "BOOM!"