Boy you opened up a can a worms!
For your first AR, go down to the gun store and buy an M4 style carbine with a collapseable stock and removeable carryhandle so you can later put on a reddot or scope.
Barrel should be chrome lined, with a 5.56 chamber and a standard flash suppressor.
Bushmaster, Rock River Arms, S&W, Stagg, Colt, are generally available in most gun stores and super sporting goods stores. You really can’t go wrong with any of those, and they’ll have warrantys if you do.
You’ll end up with a civilian variant of rifle that most of our armed forces use, which means parts, ammo, and magazines will be available and easy to find for decades to come.
Magazines. I’ll just say Magpul PMAG. Get the Pmags. Doesn’t matter if you get the ones with the window or spend a couple bucks less and get the windowless. They work, and they are inexpensive.
Let us know what you do?