depends on what type of fish you have and now densely planted your tank is, rcs might not be able to survive in there. Alot of fish that fits in a 55 gallon will eat the shrimps =/.
If you are lucky and your tank is stocked with non shrimp eating fish, then you should get whatever amount you want to have. Because there will likely not be much breeding happening in a community tank. They will have babies, but the shrimplets will get eaten. Any fish with a mouth large enough to eat a shrimplet, will eat it. So if you have fish over 1 inches, you will likely get very little new shrimps from your original shrimps. So just buy whatever you would like to have.