I would think that 6 cards is enough, although I know some people on this board seem to carry much more. If I were you, I would just take good care of what you currently have. I have 3 individual and 1 AU; for me that's enough.
You have both bank and store cards so you should not worry about the credit mix. Do you have any installment loans? If you don't, then maybe you should consider an installment loan rather than another credit card.
I agree with Baby Blue: you have a great line-up there, and it sounds like it works for you.
Many people here have a lot more cards because they started with weaker cards and had to slowly work their ways up. All your cards sound like keepers, though.
You are currently fitting the profile of the "FICO High Achievers" (thread linked in my siggy.) That should comfort you that you're on the right track!
* Credit is a wonderful servant, but a terrible master. * Who's the boss --you or your credit? FICO's: EQ 781 - TU 793 - EX 779 (from PSECU) - Done credit hunting; having fun with credit gardening. - EQ 590 on 5/14/2007