well, this is only my personal opinion, but if you really have the setup you say you have and the water parameters could be considered "optimal", then i would say you could add quite a few corals to the tank all at the same time. the only catch is to have a well-established tank with plenty of biofiltration media (which you seem to have). the only other suggestion is that you add phytoplankton, preferably DTs live marine phytoplankton (as opposed to dead, preserved phytoplankton live Phytoplex from Kent) to feed the corals that are planktivores. other than that, i feel that if you add a reasonable number of corals and feel that your tank is mature and can handle the additional bioload, you should have pretty good success. hope this helps
also, stay away from stony corals at the beginning, if you can
they tend to be a LOT harder to keep in a relatively new tank than softies
