I wouldn't recommend slow or long finned fish together with crays. They're instinct drives them to catch whatever comes near their cave/hideout/mouth. I used to have 5 species/types.
Some crays, like red claws that is said can grow over 12" (body only) are more docile if they've never tasted fish before they reach 6". They're more aggressive when young/small. I once kept 6" crays with live bearers, barbs and angelfish and they would let the fish "clean" them. But once they've tasted flesh (they weren't fed during the 2 days while I was away)- that's it, no more community.
Other species are more aggressive and will always hunt. In fact some individuals would only eat fresh fish or starve to death (caught from the wild - IME).
Tank size should be at least 4x body length, hiding places (specially if there's more than one cray) and pumps. Small 1/2 - 1g tanks aren't suitable for adult crays (small species grow to 4 - 5" body only). Some like to climb, so lids should be used (they can climb up air line tubes or even aquarium seals). I suggest water filled only 2/3 of tank because once they're out of the water, they often would stop climbing (not always).