Can you put other species of morays with him or same species only?
Sure you can...at your own risk, of course. (believe me there are folks who disagree with me on this!) I keep mine with a big green and a blackedge.
So, SO, so, if I can't have any other fish with this eel, no crustaceans, no corals, is there anything I can have in this tank with this critter?
They're too aggressive for corals, and will just keep knocking stuff over.
I use a cleanup crew in my eel tank, even though they eventually become tasty morsels for the eels. I'd say if you add crustaceans, add the cheapies--snails, etc....that are good to clean up detrius from the tank floor. I also have a cleaner shrimp in mine for the eels, but not all eels will tolerate them. Mine happen to tolerate them, which is lucky for me, since they are about $35 bucks a pop.
I've had bluelegs, scarlet hermits and turbo snails in my tank...and many of them last quite a while before they become lunch. They're so good at keeping the tank clean, I think of it as a necessary expense.