I have a South American Puffer. Sap for short. They're a bit hard to find now, and I'd like to get 2 or 3 more because they do better in a small group, but i'm stuck at the moment. Anyways, the Sap is a FW
puffer that only grows to about 1.5 inches or so. Feeds on Bloodworms and snails in the tank. Pretty social/tolerant of my other fish too. He did kill/eat a dwarf gourami, but I blame my roommate for not feeding him correctly while I was on vacation.
As to your questions: GSP are brackish, so if you made the 88g tall a brackish tank you'd be ok with them. I've heard in adult hood they prefer full salt water though, so IDK what your plans are, but you'll have to consider the adult state. They're also around 4-5 inches, or at least that one as the LFS
was a mutant...
They're also suggested to be in a species only tank, because of their aggressive nature, so you might not be able to keep any other fish...but i bet if you found some of their natural co-habitors in the wild you could keep them. Another important thought is to the decoration of the tank. In the wild the SAP lives mostly in the direct current of the rive they're found in, so they appreciate current in a tank. Not sure about GSP or the dwarfs. They also need a heavily planted tank, or a least a lot of line of sight blockages. This keeps them from getting too stressed out, or too bored.
The SAP, and the dwarf puffer for that matter, can be fin nippers, and a little aggressive, but in my case it only relates to their hunger. Fed=happy=no missing fins. I've got Gold barbs, balloon mollies, lyre tail mollies, tetras, a SAP, botia, cory cat, and albino pleco together atm in a heavily planted tank, they do fine. They biggest worry is actually boredom. All puffers suffer mightily from an addiction to excitement i suppose. Mine just pace the glass most of the time. Feeding they perk up, and I know the sap loves when i start redecorating. Thats the only time he'll come and explore the rest of the tank. Other than that its back to the corner.