My advice: Skip the cheap reflex sight. Use irons for now and save up for a good optic. Vortex makes some very nice stuff for a very good price.
DPMS makes a decent gun, a lot of people like to look down on them but for 99.99% of shooters it's just fine. Personally I think Palmetto State Armory is the best out there for the money. I've put together a couple of their kits and handled some complete rifles and they're very good quality, for the same price as DPMS.
I personally wouldn't want a bull barrel AR for anything other than bench shooting or prairie dogs. My 18" SPR barrel is a little on the heavy side but it's just right for me. Still a lot lighter than a bull barrel, and it kills the dogs just fine.