Weightlifting shoes is all you need.
I think it's a good idea to get a couple private lessons to make sure you have a good understanding of the lifts along with squatting correctly; preferably with a trainer who specializes in weightlifting instead of just learning the movements on the fly during the CrossFit class. If you do HB squats as well as flexibility/mobility work, the range of motion will come.
I had reconstructive ACL surgery and have been HB squatting every since. Then again, I did have an athletic background prior to that injury. For any questions regarding your knee, I would refer back to your PT for some tips.