That is something that we are discussing... "What defines a squad in Combat Challenge?"
We might be rewriting a few things for Combat Challenge. Stay tuned.
I'd say 3 or more at one time.
Just because a squad has a large # of players doesn't necessarily mean they will have a good K/D. They most likely will have the most kills but they will also have a greater loss on the field. Playing with less players
may give you a high K/D if you get a lot of kills per sortie but you will still have a lower kills #. Therefore, having a huge squad would give you the most kills and a lesser K/D but a small squad would give you a better K/D but not the most kills.
I think it is pretty fair for the most part because if you had a medium amount of squadies on, say around 6 or so, and you reck havoc, you will most likely get the most kills and have the best K/D.
I think the individual stats are fine.