A: Hundreds. Easily hundreds. Maybe more. It's really only a matter of how tightly you mash them in there.
What's that?
You want them to be live fish?
Well, that changes things then, doesn't it.
You know, you really should have mentioned that you wanted them to be live fish. You should have led with it. Your question should have been "How many small, live fish can you have in a five gallon tank, sir?"
You disgust me.