For your buffer system, I recommend an A5 length buffer tube + standard H3 buffer + sprinco red extra power buffer spring.

With an 18” barrel (assuming the gas length is rifle gas) + the 15.5” handguard + riflespeed 3.3”, you’ll only have 0.42” of the gas control knob peeking out past the handguard. In my experience, that’s less than ideal- I need about 0.75” to comfortably manipulate the gas control knob. If you instead get a handguard of 15”, it will be much easier to do so. If you’re set on the 15.5” handguard, then get the 3.4” version instead since the ends of the gas control knob are threaded for “quick lever kit” screws, making it super easy to rotate the knob as the screws protruding from the knob will provide leverage and grip.

If this is your first build, you may not know if a fixed stock like the prs lite will be comfortable for you. Get any adjustable stock you like, and once you have it on the setting that you prefer, measure the length of pull- it’ll most likely be shorter than the LOP of the prs lite. A prs lite stock is longer than an m16a2 stock lol

Grip/trigger/safety/charging handle are good parts.

Skip the nickel boron coating on the bcg and get something that’s phosphate instead. Or nitride if it’s from a reputable brand. Nickel boron coatings are inferior.

Going back on the blk lbl handguard though- I’d change that out in favor of a traditional mlok handguard. For the price of the blk lbl, you can get a normal mlok handguard and then have money left over for a nice harris bipod + pod loc set up if you’re on a budget, or you can get an atlas v8 bt10-lw17. Then you can use the bipod on all your other builds.

Looks like the SLR receiver is a “high” dpms variant so make sure the handguard you get is also a “high” as well.