My $0.02… Shooting 5.56/.223 always go with a 1/7 twist. It allows you to take advantage of the full range of commonly available weights from the heaviest 77gr down to the lightest 40gr varmint rounds. (there are some boutique rounds outside that range but i wouldnt worry about those).
A “slower” twist of 1/8, 1/9, or 1/12 will generally have trouble stabilizing the heavier bullets but will be fine for the lighter bullets. If you go with one of these, just be aware of what you can/can’t shoot through them.
I have seen people on the internet saying they’ve seen other people on the internet saying you can spin the lighter bullets “too much”, but i’ve personally never seen any evidence of that in person or otherwise.
As far as brands for a completed upper, these would be my recommendations that I have some experience with:
Sons of Liberty Gunworks
By reputation, I’d also recommend a look at
I’m not familiar with Yankee Hill Machines specifically, but there are lot’s of good manufacturers making good equipment (and also some junkers). Do a good bit of googling online for reviews, or Youtube reviews by known firearms reviewers as they can put it through it’s paces better than most of us ever will.
I’d also add… are you sure you want a quad rail? They are typically noticeably heavier than MLOK (or KeyMod) and MLOK can give you similar number of mounting points.