here's my crazy suggestion:

optional: buy a new complete AR so you have a working one to see how they work.

not so optional: watch a bunch of youtube videos on how to assemble the lower.

buy a lower at your dealer as described above... or buy 2 or 3

buy a PSA upper with a lower parts kit, they have one on sale today, every day...

build the lower using what you learned in the videos. You might also want to buy a few tools: the roll pin starter punches, regular punches, the wrench for the buffer tube castle nut, Wheeler has a nice tool for the trigger guard pin.

buy a bunch of magazines, some optic (PSA will have that on sale too, if not today, later this week)

buy a case of 55gr brass case ammo (everyone has that on sale this year)

go have fun!

later you can build another, you got more than one lower, right?.... and then another.... eventually you'll get bored with .223/5.56 that's OK there are a coupla dozen other caliber options.

WARNING! these things are addictive

Poole