The handguard has been chosen

Came with its own barrel nut, proprietary design

This is a Diamondhead VRS T-308L.  Free-floating, 13.5" long, fits over a low-profile gas block.  Instead of the standard 'torque the barrel nut to minimum, then add enough to line a hole up with the gas port in the receiver', this barrel nut uses a 1 3/8" wrench to tighten it down, and is low enough that there's no obstruction of the gas port.  Then the handguard(forend, whatever) slides over, two bolts go through it and cutouts in the nut, level it and tighten the bolts down.  Lots of good reviews, and it's not a tactical cheesegrater design.  I wanted something with a flatter bottom instead of round, and this feels good in the hand.  And you can add rails to it if you wish.  I think it'll work nicely.

Also have a gas block and tube, and a vise block for the receiver.  Waiting for the crowfoot wrench to come in, then I can hook it to the torque wrench and assemble this.

I've never built a AR before.  My LORD, the options...