I have a pair of dwarf cichlids (rams) in mine... they're really nice and colourful, but i'm gonna get some dither fish to make them more active. that much said, they're gorgeous and if you're just putting them in there you can put 2-4 in a 10g.
dwarf puffers get about 1.5" big at the most. They MUST be fed snails on occasion to file their teeth down (or else their teeth get too big) also eat brine shrimp, frozen and live bloodworms. beware=fin nipper.