Pretty good synopsis. I would add buying the BCM LPK with their PNT Trigger gets you a very good parts kit, and a better than average Mil-spec trigger for not much money!I'm in the middle of an Aero build. Amazing fit of upper/lower-- better than my DD, actually.
I'm right now spending a lot of time thinking about where it makes sense to spend money. There are lots of things in AR world that you can spend money on without getting much (if anything) in return for the premium above generic mil-spec.
Mil spec triggers suck at pretty much everything except durability. Every penny you spend in trigger upgrades gets you nearly zero in reliability or durability. For a match rifle, that $300 trigger is surely worth considering. For a combat or duty rifle or SHTF EOTWAWKI rifle? Save the money. Or go cheap with an ALG or similar.
Buttstocks, too. Spend as much as it takes to get a well-made one. More adjustments and screws and "features" are often failure points. Maybe a basic fixed A2 isn't so bad? The new BCM looks like a winner and is only $60.
Do you really need a $300 handguard full floated and all that? Yes, if you have to have ultimate accuracy. But if you are OK with minute-of-man, probably a basic USGI arrangement will suffice. This is an easy area to save some cash.
Likewise with muzzle devices. Everyone has a favorite. But you will never beat an A2 birdcage for effectiveness-per-dollar. As a flash hider, it works. And if you *need* a brake on a 5.56 gas gun, you probably need to work on recoil management.
Where to spend money then? IMO, barrel, bolt, bcg, and gas block is the place to splurge enough to get a good one. Arguably, you need not go big dollar on the barrel. Maybe a Faxon is just as good as that $300 FNH. But there's a world of difference in reliability history between them. Maybe that's worth it.
Gas blocks seem to be an endless source of function problems. Get a good one that's installed PROPERLY and you'll not regret it.
Another place to spend money is probably opting for an A5 buffer setup. The improvement in dwell (and hence reliability) is great, and shooting smoothness is way better. Score one for a system that offers really no downside but cost. And with the BCM A5 setup, it's hardly a big-spending endeavor.
Every build I attempt in the future will have A5.
Likewise, if you this is a hell-and-back rifle, you can't pretend your Bushnell TRS-25 is as tough as an Aimpoint. And your irons better be decent ones that can be trusted absolutely. Yes, troys weigh more, but if you can't aim, you can't hit. Don't cheap on the irons.
The converse is also true. For a plinking toy, that Primary arms or Strike Eagle is just fine. Plastic MBUS are OK. No doubt, that faxon barrel will serve well.
ARs are like tires-- one that is setup to be the ultimate in one thing will suck at the others. Race slicks suck in wet weather. Off road tires are loud and don't last. A cheap rifle isn't the toughest or most durable or the most reliable.
We've all heard that maxim about "fast, good, or cheap, pick 2."
But in the AR world, it's "weight, accuracy, reliability, or cost, pick 3"
Sorry for the rambling stream of consciousness..