School me on go to 9mm AR parts

[Vegas]

Hey all,

Been thinking about a 9mm build for a while and finally ordered a New Frontier Armory C-5 lower (accepts MP-5 magazines). I'll be adding their upper receiver for compatibility with the mags but after that, I don't know squat. Some I am wondering what are the go to parts as far BCG, buffer, spring, receiver extension and barrel? The build will be a pistol configuration with either a SBA3 or Tail Hook Mod 1.

C5LOWER.jpg

Thanks in advance.