Everyone has their opinions:
I think the price is very good. Bushmaster had a recent price increase. What you saw last year doesn't apply.
I wouldn't own an AR without a muzzle brake. The AK is one of the louder muzzle brakes. I personally don't care, but that is personal choice. The AK brake is also one of the more effective brakes out there along with the Mini-Y comp. If you want another brake, one of the best places to go is Kurt's Kustom Firearms
http://www.kurtskustomfirearms.citymax.com/page/page/8932.htm . He has a variety of brakes and does the install. Don't buy something with set screws, this is mickey mouse. Do it right.
http://www.ar15.com/forums/topic.html?b=3&f=118&t=155969
Before someone chimes in here saying that the AR15 doesn't have enough recoil to justify a muzzle brake; this isn't about recoil. It is about muzzle flip or put another way, the ability to fire rapid shots with accuracy. If you don't think they are worthwhile I invite you to do some El Presidente's with a timer and see what you think. Muzzle Brakes are not flash suppressors, but they do reduce muzzle flash. I have watched a demonstration of rifles being fired at night with various flash suppressors and muzzle brakes. One of the worst was a 16" barrel with nothing on the end. There was a huge fireball.
Accuracy; the AR15 is a superbly accurate rifle. The one you are looking at is a superbly accurate rifle. Just as accurate as a bolt gun. Even though you arn't looking for extreme accuracy on targets, you will have it anyway.
Bushmaster. IMO the best AR15 made today and as good as any that have ever been made.
Magazines: Stick with USGI magazines. Others probably work OK, but this is the best mag out there for civilian use. HK makes a better one that us peons can't be trusted with. I buy my mags from CDNN Investments. I have both 20s and 30s. I see no drawback to using 30s except off the bench. The only problems I ever had with an AR15 was when using a 40 round mag. The ones I have don't run well.
Barrel Length: On my rifles, using my chrono, the difference between a 14.5" and a 16" barrel is an average of 78 fps.