OP, a couple of pieces of advice. Don't replace anything you have bought with anything mentioned in this thread until you have built the rifle and have identified an issue or need that said part addresses. Second, if you are prone to analysis paralysis, turn off the computer now- you're only going to get further from your goal with this thread, and spend more money with no rifle to show for it.
That said, I second the recommendation for the SLR gas block, with a caveat. The .936 diameter block i got from them required a straight gas tube for my ar15 build. I've not seen a +2 straight gas tube.
I used an Odin works adjustable gas block in a recent build. All of the functionality of the SLR, at a lower price point.
The Larue MBT-2S is a very intriguing trigger. But, the Giessele gets to that 3.5 lb break using full power springs. For $80, I don't think you can go wrong with the Larue, though I've got half a dozen Giesseles.