First thread from a newb?...Need advice

[Whelenon]

All the answers to your questions can be answered on this forum. What you're looking for is easily achieved with the Grendel, I'ld recommend an 18" barrel for shooting 4-450yds. If the RRA .223 is a standard AR-15 all you need is a Grendel Upper. I built mine for hunting and it weighs 7-1/2lbs w/scope. Go to the photo section, there're a lot of examples of how some of the guy set-up they're rifles. The big question you need to consider is how much do you want to spend? Do some looking around, complete upper are available and if you want to build, parts and components a can be bought without need of an FFL.
Keep asking questions, plenty of guy here willing to help, welcome to the board.