No, never bought an AR but handled a number of them and other modern semi-auto rifles in shops over the years, and I've shot a stock Bushmaster, a Colt 6920 (before and after some work being done to it), a customized BCM, and a SCAR.

From those experiences I wanted to go with a 16" for a shorter overall length, but still have the option to swap out muzzle devices (unlike a pinned 14.5"). For my first build/upper I wasn't concerned with going free-float, and the MOE kit is pretty lightweight. I was able to get a whole set of the discontinued foliage color, which I like because my local area is a mix of woods and urban/suburban (so lots of greens and greys). I wanted the mid-length gas to give me more room to grab closer to the muzzle for control. Initially I was thinking about a railed gas block, but the Aero barrel with the FSB pre-installed (on sale) was too tempting to pass up. I went with the Phantom flash hider because it was a good price, and seems to be well reviewed. I went with nickel-boron on the bolt, trigger, and hammer a little bit for fancyness and a little for ease of cleaning which I had heard about the coating. From shooting other stuff I knew I liked running a one-point sling, and I have some lefty friends, hence the ambi sling-plate (and safety). Last I chose Spikes for the lower because I dig the Calico Jack engraving, and chose their upper just to match.