Generally, since they brackish, they need the Specific gravity to be around 1.005. That being said, they need brackish tank-mates. So, Mollies, Scats, Monos, Archerfish, bumblebee goby, and other GSP's are possible tank mates. Just be cautious when housing them with any tank-mates (besides their own kind), they are known to be aggressive fin-nippers (really, I think a species only tank would be best).
Since they get 6" , they need at least 30 gallons to housed in. They need a already cycled aquarium to be put in, they are very sensitive to any trace ammonia and nitrite, and need low nitrates.
The diet of the puffer should be varied. You will need to supplement their diet with snails no bigger than the size of their eye (the shells of these snails will wear down their beak-like teeth, which would grow so long that they would no longer be able to eat.) and meaty foods.
Hope this helped.