Welcome to the board.
Your answer depends on the fish. You could say put up to 5 small to med fish in there. Example 2- clowns, 2 blue/green chromis, and a firefish.
But you would not want , 2 maroon clowns, a lionfish, a tang and a foxface.
Equipment. I had 2 double cartridge whisper filters, 2 maxi jet 1200's and a heater. I would also suggest as filtration getting some live rock and using the correct sand at about 2 inch depth, and instead of the MJ 1200 you might want to go with the MJ 900's instead, the 1200's are power hogs. A skimmer would be very benificial. Stay away from skilter filters.
Thomas