If you want flexibility, zeroing at around 50 yards should give you the flattest trajectory, about +/- 2.5" from 0-225 yards. Otherwise zero at the distance you'll normally shoot.
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