DO green puffer fish need salt? What other fish could possible go with green puffer fish?

Answer 1

Yes they do - and in increasing amounts as they mature.

All puffers tend to be territorial and aggressive. There are a few species that can be kept as groups of one male and a few females of a single species, but others should be kept as a single fish. You can't determine gender on these, so you may be risking aggression to try and keep two in the same tank. One of the links below (2nd) suggests keeping them with Ceylon puffers, but these aren't a typical puffer you'd find for sale. The 3rd says to keep them alone.