If your water params are all in check, you might want to try a small piece of coral or a small hardy fish. Since you mentioned that all the clean up crew is doing well so far, I'd say you're likely ready to begin adding (slowly) your livestock. Plan everything out accordingly, though. Some fish are more sensitive or aggressive and should be added last. Test the water before adding anything, since you've added livestock it's possible that there's a small NH3/NH4+ spike. To reiterate, whatever you add make sure it's done in small increments.