I have 2 fig8s right now in my 50 gallon brack tank (until my salinity gets too high for them). I'm currently at 1.0010. like most puffers they can be nippy at times and are best suited in species tanks when they mature. when young they can be kept in groups but eventually, if they don't have enough area, they will bother each other.
all puffers need to eat the occasional "hard bodied" creatures. like snails, shrimp, crayfish/crawdads, krill, crabs etc... I feed my puffers ~a dozen snails a week and occasinal baby crawdads. as far as daily foods, I use freeze dried and frozen krill, bloodworms and brine shrimp. they will occasionally eat flake food if its moving in the current, but I don't think that is enough food for them.
HTH
edit: Jamison, there are several completely freshwater puffers. Dwarf puffers, T. Fahaka/T. lineatus, C. Asseslus are a few that come to mind.