I chose an 18-inch Lothar Walther barrel from Spike's Tactical.

I desired a 20-inch barrel for ballistic efficiency but couldn't find a vendor to provide a semi-stripped, 20" LW barrel. LaRue Tactical does offer LW 20-inchers in complete uppers.

Weight isn't a huge concern for me, so a ~.750-inch diameter has worked well. It is very accurate.

Having "grown up" with the M-1 and M-14/M-1A, any Stoner AR is "light" to me. If weight is a concern for you, don't forget that ounces (pounds?) can be saved with careful selection of other components, especially the stock but also in the forend and sighting devices.

The toughest part for me was selecting what I wanted to use! Good luck with all that!!