you could have lots more if they have enough hiding spots. IF you keep the bioload in check through proper filtration and IF they get along. theoretically you should just add one fish at a time, wait a month and see. the other theory is that the existing fish will already have established territories so you have to rearrange the rockwork. then you have a better chance of them getting along, but also a small spike due to the stirring up of the tank.
good luck with those damsels