If 90G is what you have and you want them for life then my recomendation would be to do a brackish tank.
You could get Green spotted puffers that are a lot of fun.
The only problem is they are born in fresh, then move more and more salt as they get older until they are full marine.
Tankmates could include any of the four types of scats (green, ruby, silver or striped), any of the archers fish, monodactylus sebae or argentus (gorgeous fish), the FW snowflake eel (can go full marine), the knight goby, or another awesome fish with tons of personality the butis butis or as commonly called the crazy fish.
I have always kept GSP in pairs and they tend to swim with each other which is alot of fun to watch.
If you get scats with them be aware that they are messy eaters and will need really really good filtration since puffers are vulnerable to medium-poor water conditions.
On my puffer tanks I have at least three times he needed filtration on each tank. May be overkill but I love my fish.
Live plants may be out of the picture with many of the tankmates above, but I would make sure to add plenty of fake plants or other decorations for the fish to hide and swim arround in. My butis love drift wood and blend into it perfectly (normally at wierd angles).
These fish have tons or personallity, are absolutely gorgeous, and will be very rewarding if you choose to keep them.
Good luck on your puffer quest, I hope you will join us.
