RE: considering purchasing an AR-15 at some point in the future
I'd make sure you really want one. I've had three and the thrill is gone. I find them to be very unreliable. After you shoot a few thousand rounds through it and all your friends have seen it and have gone ohhh and ahhh it will be an 10 paper weight.
If you decide you need one build it yourself. It's very easy.
Tom