Well you're smart to research before buying. Definitely get up to speed on CA compliance too.
I'm pleased with my 16" midlength lightweight uppers. Lighter is almost always better and getting weight off the front of the rifle makes a big difference.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
US Army 1966-69, VFW Life Member, Retired Geek