you would be fine with anything with a shel(hermits, small snails as they cant get thier mouths in them and the like)
i have had a puffer. and currently own an eel. the eel NEVER goes for any inverts that i have seen
the puffer on the other hand would wait for one to fall and then strike lol
for left over food particles try damsels or a fast wrasse. i have an urchin with my niger and some damsels, dont have a problem yet.