the club fan shop is definately open at leoforos, you can go there and buy shirts, scarves, jackets, etc.
as for stadium access for photos, last time i was there i just found an entrance open, walked in and took some photos. i even managed to get on the field and no one noticed i was there. i dont think anyone would of cared really.
i believe the basketball courts and pools are still used, and possibly other facilities as well but not really sure.
going to painea was harder though. i know they have a museum type gallery there with trophies and memorabilia but i couldnt get access....i went there after i found a taxi willing enuff to drive me there (after half an hr of looking for one in centre of athens) and all i got to see was a bit of the training pitch and that was it
but worth the drive as i prolly will never do it again!