I love Elephantnose fish. They're a mormyrid, like the black ghost knife or the 'baby whale' fish, which means they've got a radar-like system of detecting things in the water. Mormyrids should generally never be mixed -- though, as you mentioned, you can keep a BIG group of them in a BIG tank.
The elephantnoses are probably the best mormyrid out there for most aquariums. Depending on species, they don't get particularly big, they're not aggressive, they're not fish eaters, and ... they don't hide all the time. They should be kept over a fine gravel or sand of some sort, as they can damage their noses on rough gravel. Feeding can be tricky at first -- sinking pellets, live blackworms, etc. Usually, they'll quickly learn to eat other foods, and providing you aren't feeding exclusively floating foods, they'll do just fine. They'll even eat flakes (add them to the water column, do not toss on top!).
One other big word of warning. They prefer dark tanks, and need shady areas to escape the light. They'll stress to death in a brightly lit tank. You can keep them in a brightly lit, planted tank, provided they have things like large plants, rootwood, etc., to shelter under -- just make sure you feed them after the tank lights are out.
JW