I don't know why people think the take down detent pins are hard to put in. I just put the spring in, put the detent, and mash it down with the take down pin and insert at the same time. Snaps right in. I never launched one this way. Although, if you're paranoid, do this in a plastic bag because if the detent goes flying, I assure you, you'll never find that little thing.
The hardest part in my opinion is putting in that hammer. That's a little bit of a PITA because you're working against the hammer spring.
Occasionally, the trigger guard roll pin, if it is a little on the thick side, or the lower has thick finish, will take quite a pounding to drive it in. You should support the lower, because people have broken the flanges off hitting them hard.
From a general perspective, the AR lower is quite easy to put together. Certain operations on other firearms are significantly harder. AR is cake.
If you get a collapsing stock that has a castle nut, spend the money and get the proper wrench. You'll do less damage and get it tighter.