Help Me Finish Out This Build (Qs in comments)

I'm very close to finishing my first build but would like some input on the last few components. Before I get into them, here's the build so far (mockup image attached):

Lower (already assembled): Tennessee Arms Lower with CMMG LPK Anderson carbine mil-spec buffer kit Magpul MOE mil-spec carbine stock Magpul MOE Gen 2 30 round mags

Upper: Aero Precision completed upper with FA Black Hole Weaponry Slim Mid 16" barrel ALG EMR V1 15" MLOK hand guard Unbranded mil-spec charging handle Vortex Crossfire II 1-4x24 (no illum)

Need:

BCG * I'm not interested in paying the NiB premium at this point. Will a PSA BCG hold me back materially in function (cycling, accuracy) of the rifle?
* Is there something else I should be considering in that price range?
* Do I need a nicer BCG to get the most out of my barrel?

Optic mount: * other than saving a few oz, does the Aero ultralight give me any advantage over the Primary Arms mount?

BUIS: * This is a coyote rifle so I will buy these only after everything else is GTG

Gas Block: * I'll be installing this myself. I think based on reading I want a low profile (.750 to match my barrel) non-adjustable block with set screws. Is there a better way?
* Based on previous bullet, where's the bag for the buck (what part do I want, and where should I buy from)?

Gas tube: * I prefer the look of a nitrided gas tube, but would consider one without costing if there were any advantage. * Do I care about who made it or just get the right length and call it good?

Muzzle device: * local RRA dealer has an A2 cage at $6.50. Do I need crush washers or are they more for a device that needs to be timed?

Other: * am I forgetting anything else essential?
* I'll probably get a light on this eventually but I'm not in a hurry
* Not planning on a bipod for now but will have shooting sticks when I'm hunting.
* Is there anything I can do to tighten my stock if I don't care about collapsing it for now? I realize there's a fixed MOE stock and other fixed options, but I'm curious.

Fixed for formatting

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