There's no minimum so to speak, seeing that you are in Florida, you don't have to worry about the fish freezing out. The water might get too warm if it's too shallow, but I think you'll be O.K, with the 4'-5' depth. I'd be more concerned that you had enough O2 in the pond. But, if you keep the fish numbers low, that shouldn't be a problem either.
RES = Red Eared Sunfish. They are recommended for swimming ponds because supposedly they "nibble" at people less. BG don't have teeth that you have to worry about anyway.
fish acronyms