Leleupi are a bad choice to mix w/shellies, they tend to tear them up from what I've read on a couple other forums. Multi's would be a better choice if you want to breed and raise the young in the same tank. The non-colonial species aren't nearly as good for protecting their fry after they're free-swimming. Also more interesting when their numbers increase, and the whole colony protects their territory.
If you want a really interesting fish (and can find one for a decent price) get a plagiostoma spiney eel. They're few and far between in general availability, though there are some listed on aquabid at a bit more than twice the regular price. Elipsifer eels are also great, but will outgrow a 55.