I have 5 Eels in my tank and they all co-exist nicely with my lionfish and bamboo shark.
Tight lid and most definately mesh up your intakes for overflows and intakes as my snowflake likes to scare the hell out of me by jumping into the overflows and landing in my sump.
i also have tones of rock work, make sure that they can use these as tunnels, and make it so that its facing the front of the tank, otherwise you wont see much of them during the day for they usually stick out 1/3 of its body from their cave.
Sand also i find is a good thing and not to go bare bone as they like to borrow under rocks.
Our LFS has just recieved a nice shipment of 8 Eels which i more than gladly helped put in the tank
Any more Eel lovers here?