You've got plenty of room for a porcupine puffer; they get to become real "pets". Tons of personality, eat anything,love attention, inexpensive, etc. A Porcupine Puffer always becomes a favorite; up front, begs constantly. Unfortunately, most folks don't realize how big they get and end up in keeping them in tanks that are way too small. Any of the Arothron puffers also would be great. Really, with your stocking plans, even the small puffers would work and you can get what YOU want---and that's the way it should be. Puffers should be de-wormed and need hard foods, like shrimp in the shell, to keep their teeth trimmed; but they generally are hardy and long lived.