when the tank is done cycling I would add some LPS corals....but you will have to monitor all your levels and perform all the tests.
I would get a torch, frogspan, or hammer braching coral...definetly a brain coral too...these are more difficult than the softies and polyp corals though...
Mushrooms would be easy but would have to be placed in a lower light place..I bleached my shrooms out when I had my vhos on them...yellow polyps, star polyps, daisy polyps, and the various leathers are also fairly easy...
xenia are cool to, but more difficult to take care off...
maybe you could add a few easy sps like a birdsnest...