In my 90-gal fish-only tank, we have a porcupine puffer and a fingerprint toby. No shrimp, no crabs. My puffer got ahold of my Sally lightfoot and made very short work of it. My cucumber and certain starfish are ok, but I wouldn't recommend putting serpent stars in, as they may hold some appeal, and they have no defense. Puffers will eat almost anything you put in. And you don't really have to cut the shrimp up, they will chew it into pieces. I just drop a few whole frozen krill in and within a few minutes they are all gone. They are very interesting to watch, and very intelligent. After time it will associate it's keeper with food, and will "beg" at the front of the tank any time you are in the room. Also, do you have any type of cleaner wrasse? Puffers are VERY prone to ick, so you may want to consider it if you don't already have one. Good luck!