The reason I say elaborate is because, depending on species, crays can be territorial and cannabalistic. The newly hatched/detached larvae even more so. Therefore, alot of space and hiding spaces are required to maintain them to adulthood (feeding-size). Males are best kept in a 1-cray:1-tank setup until you want to breed them to a 4-female tank. Then the breeders have to be separated. Once females are berried, they need to be separated out.
Small 1.5" dwarf crays can be kept in a community so long as the tank is a good size. A dozen breeders can be housed in a 55. But, again, berried females have to be isolated and the larvae raised away from adults.