Q1: no, you have to be entering the lounge, and you can bring 1 guest.
Q2: no
Q3: yes, although in CDG they enforce that you HAVE to go to the lounge in your departing terminal
Q4: see Q3
Q5: flyertalk has threads on guesting people. However, at least in CDG they check that your guest is on the same departing flight as you are
Q6: see Q3