Species specific sea horse tanks are awesome - blue stripe pipefish would be sweet for that...they'll do their dance - the 16 gallon should be just enough room for them, I wouldn't go smaller - and prob would do better in a 24...but if it was only then and maybe some
Sexy shrimp...might be a sweet little peaceful thing to look at - the sexies should be too large to eat, they're pod eaters anyways...