Forget the details. Just get a lower or two or three, and build them up how you want them later. The lower is considered the firearm by ATF so your foot is in the door. Cost should be under $150 each. Everything else is just an unregulated parts. They build easy with no special tools, anyone can do it.
“Just get a lower or two or three”
got the last few there at my shop - 160 each