The first thing I would do is take a look at the Stickied Threads at the top of this section. You will find several very helpful threads, some of them from people exactly where you are now and the builds they ended up doing themselves.
Of the parts you listed I don't see a reason to spend the extra coin on a NM 2-Stage trigger in a 16" Entry style gun. You aren't getting the true benefit of the 2-Stage as it's designed to be more of a target/varmint/tactical shooter support style trigger. 18", 20" barrel, longer range sort of thing.
MJ and Quentin love BCM, so don't be afraid to check them out, but don't narrow your focus too hard, it can cause eye strain.
As for what to look for in a lower. This has been discussed quite a bit, but as I like to poke the Interwebz Trolls, I'll say it:
A lower, is a lower, is a lower. Unless the lower is made from scrap lawnmower parts from Cletus' Garage and AR Accessoriez, you are going to be getting a simple part that holds all the components together.
I have said before I could build a lower out of plywood and get the gun to fire. Durability would be a problem, but really all the lower does is hold parts in close formation.
There are three types. Cast, Forged and Billet.
Billet is the most expensive, the most coveted and the biggest OVERDONE of all the lowers. They are the Ferrari.
Forged are pretty much the most common. They are everywhere and more like the F-150.
Cast is kind of the taboo, is it or isn't it, element. Opinions vary with this one, but if you get a good one, it will be fine. If you get one of the last ones they made before they scraped the mold and started a new batch run.... well, maybe not so much.
Here is a very good write up between the Forged and Cast done by Olympic Arms. Yeah, those guys, the ones that will leave you dead in a ditch if you buy their weapon according to SOME websites.
Olympic Arms, Inc. - Is my receiver cast or forged?
Good luck with your research and PM if you have any questions.