The magazines will be determined by the lower. It will work with either Glock or Colt style, so you can choose your preferred lower.
This kit contains everything but the lower. The lower will need to be acquired separately.
Yes, the BCG and charging handle are included.
This will work with a glock style lower and mags.
The muzzle thread is 1/2x36.
The barrel twist rate is 1:10. The inside diameter of the handguard is 1.365". The upper does not have LRBHO.