red clawed crabs are easy to care for.
they require brackish water and a tank of atleast 3g per crab. The tank should be 2/3 land. and the water heated to around 26 C
they eat anything, fish pellets, prawns, fish, plants, bloodworm, dead fish and even dead plants from another tank.
i don't recommend keeping them with fish, they are better off in a species tank.
the tank should have plenty of hiding places. sand is the best substrate in my experience.
let us know how you get along.