Hello!

[battlemidget]

Check out Ballistic Advantage, they make good barrels and usually have good availability. If you do a 14.5" with a pinned muzzle device to get you to 16", that's a popular setup. Faxon has the 'gunner' series barrel in 14.5" with a factory pinned muzzle device to get it to 16", they're decent but they do open up (meaning your rounds will spread a little) after a fast mag. On the plus side, the gunner series cools down very quickly as it's normal to the gas block and then thin to the tip.
For the pin job, I suggest Oasis Customs off of Fillmore. He's fast, and he's more of a smith than a gun dealer.
If your buffer is carbine length I'll suggest you go with a heavier buffer too, H2 is a good weight generally speaking. In my experience, adjustable gas blocks don't really tame down felt recoil that much, but they do cleanup your bolt quite a bit. There's a company named Vltor that makes an 'a5 system' that's very well regarded.
Check out this video on buffers https://www.youtube.com/watch?v=Juy_KIPxmlI
For optics, check out Primary Arms. They're pretty decent and a good value. Holosun is getting popular too with Red Dots.
Definitely eyeball a red dot before you buy one (any red dot) to determine if your eye has an astigmatism. If the dot is anything but crisp (like a comma, or a strawman), then get a 1x prism scope (primary arms has them) unless you don't mind figuring out how to shoot the red dot with the astig.