Am I also able to use a regular BCG and charging handle with a gas system in the same upper with this system if I want to switch BCGs and shoot semi? — 2 Answers

This upper will shoot however the rest of your AR is setup -- with a properly installed gas system, it will run in semi-auto whether the side charging handle is installed or not.

The upper NEEDS a normal charging handle installed or hot gas will blow out the back into the general area of the shooter's face.

This upper functions with a mil-spec bolt carrier; HOWEVER, the side charging handle requires a threaded hole in the bolt carrier to attach. (BCGs can be bought this way, or you can have your favorite carrier drilled and tapped by a gunsmith.) The upper can function with or without the side charging handle installed. There is no need to change to a "regular" BCG -- simply remove the side charging handle and it'll look and run like a "normal" AR.

BCGs with appropriate side charging handles for this include the Young Manufacturing National Match Bolt Carrier w/Side Charging Handle and the Valhalla Tactical Side Side Charge AR15 BCG Enhanced. (I've read that the Bear Creek Arsenal (BCA) (& clone, such as Davidson Defense) side charging bolt handles widen a little too soon for the reinforced sidewalls of this upper. The location of BCA & clone charging handles holes may or may not be compatible with this upper -- I have not read either way.)