i would go with a species only tank as they will almost catch and eat anything that moves. the only fish i have had experience keeping well with crays is guppies. i lose maybe 1 or 2 a month but as there feeders i dont mind but any other fish i have kept with crays either havny lasted or got there fins battered.
i have 2 red clawed crays who are about 6" long (without claws) and they live very happy together and share the same cave even though there are many hiding plasses and caves. they were aggressive to each other at first when there about 2" , but as soon as they reached sexual maturity they fell in love an mated and they live very happy together with there kids.