https://criterionbarrels.com/media/accurizing-the-ar-15-video-series/?v=7516fd43adaa
That link has all sorts of good info.
And... if you are reasonably competent with tools , you can do most all of the videos improvements.
I will second the true the upper receiver face ( part 3 , 54 second point ).. I do it to all mine now.
Until we see photos of your freefloat tube barrel nut setup... I am not positive a "normal" Large Frame lapping tool will fit yours.( There is a special one for Aero M5E1 Enhanced ) so post some pics, please.
I am a firm believer in a snug upper to lower fit, on all my AR's... easier to have a consistent wielding of the AR.
If you are not comfortable doing some of the things... post back here and ask...
You can assemble a very accurate Large Frame AR... I have done so myself... And I am not a Super AR Gunsmith... just an average mechanically minded guy.
Bear in mind .... buy as good a respected barrel you can afford ( a bargain in these days of high cost ammo ) ... you might have to try a fair assortment of factory ammo to find one your barrel likes ( a great barrel will tend to shot a larger assortment of ammo better )
And the 3rd thing... you can already do... shoot well.
FWIW... these are a 6.5CM 10rd group, 100yds, rapidish fire, and a 308 10rd 100yd rapidish fire group. No barrel cool down ( like God intended an AR to be shot. )
I flubbed the fliers.
FWIW.... PSA PA10 upper and lower, 6.5CM Criterion 22" barrel, .308 Criterion 18" , SLR 's Adj GB on all mine... both assm'd using the Criterion Videos tricks.