I can speak a little about E-cats as I have kept a few over the years. First off, there are a few species. Some of them stay max 12", some get up to 3'. It's very difficult to discern what species is what. Second, they really aren't picky eaters. The ones I've kept have taken anything from flakes, to shrimp pellets, to fish/shrimp chunks. Onto cohabitants, well that's tricky. I kept one with a black belt cichlid and IIRC, a red terror? You could see they really did NOT like being in there with the E-cat. They would go and huddle into a corner as far away from the e-cat as possible. The e-cat would actually swim up near them and the cichlids would scramble for their lives. The e-cat didn't kill them but you could see it probably wasn't the right thing to do housing them together. Fish that MAY work with the e-cat could be smaller active schooling fish like tetras or barbs. The idea is the they're smaller and quick so the e-cat can't really get up closer to them. Plecos might also work. However, you want to make sure its a pleco that hides and that there are PLENTY of hiding places. Also, in any case, a big tank would be helpful in ensuring the survival of tankmates. Lastly, on to the shock. When they're small, you'll get a nice little tingle if you touch them. At the 6-8" mark its strong enough to contract a hand and cause you to jerk back. 12" and up, shock is probably bad enough to convulse your arm. They won't potentially kill you like an E-eel could, but its definitely not pleasant.
EDIT: I should also add they're a very personable cat. Mine would always come out begging for food when I approached the tank. Just don't hand feed them lol
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