You can have more than one, they have little to no effect on the bio load of the tank. They will clean almost everything. From substrate to decor, to filter intakes and heater bases. They shed (molt) their exoskeleton. Once you see this it will appear that the shrimp died. Keep an eye out for it but leave the molt in there. Once he does molt he will keep himself well hidden, this is natural cause their new exoskeleton is soft and leaves them vulnerable to danger. He will eat his molt to regain the nutrients lost. They don't need a specific diet, they will eat the uneaten food you feed your other fish, also eat algae and even shrimp pellets (mine love them). If you have any other questions don't hesitate to ask.