Do you want to spend $1500 for it and then buy mags and optics or do you want to have a total investment of $1500?
Is there a range near by that has some members with AR platforms.
Make a check list of things to look for like rate of twist, barrel length, sights or no sights, stocks, and accessories.
You can start with a plane Jane gun learn to shoot it and then decide what you would like to have on it.
I have probably had about 25 or 30 AR platforms over the past 40+ years. I have had a number of interesting things for them, some pure CRAP and some very simple and useful. Now that everyone is making them you don't have to pay an arm and a leg and be limited to just a Colt.
Recently I have sold two Colt H-Bars and I wanted to put a flat top receiver on one but found out it was going to be a pain in the A** to find a few things to do the job. I sold them and went back to my Armalite that I got from Richard a few years ago.
My carbine and rifle both have adjustable stocks and its great for me as I am vertically challenged (5' 5")
If you want to shoot distance invest in good optics and a good trigger system.
Don't load it up with everything you can think of, keep it simple.
That's my two nickels as we don't use pennies