I've got several AR's and only a few are not Rock River Arms. I like the RRA's the best. Their customer service has always been top notch (it is highly unlikely you will have an issue, I am a dealer) and quality is excellent.
Yup! AR's are lego kits for the adults. I will stongly agree that you can easily swap out any parts you don't like or wish to upgrade.
I actually sold a 20" Coyote to an older skydiving buddy last year and he absolutely loves it! He was slightly hesitant at first due to the cost, but after asking me questions about it for about a year (and doing his own research) he began to see all the pros (he's a target shooter) and the level of quality he would be getting. Loves it!
Very accurate rifle! I remember seeing him down at the drop zone after he took it out for the first time earlier that day. The smile on my face was almost as big as his. He had been shooting a Mini 14 for the past several years and could hardly believe the accuracy with his new Coyote. Even with a low/medium quality scope he felt like a countersniper overnight! (He chose the 20" moly bbl)
He has already upgraded to a higher quality scope and a Magpul PRS stock.
My advice would be to use the best scope you can afford, a Harris bipod, and 20 round mags. (30 round mags are to long to go prone and although 10 round mags will work nicely, its good to have the extra capacity.) Simply my opinion.