your live rock should be cured first and you will probally see an algae bloom, it will happen pretty much overnight - check your water params and if there good this is a good time to add snails, i suggest a few turbo snails (good for helping to clean the glass/rock start with maybe 4), a few nassarius snails(good for mixing up the sand bed start with maybe 4), and a few red hermit crabs(alittle more expensive then the blue hermits but from what ive been told are better at eating algaes start with maybe 2) i woudnt over do it because then there wont be much in there for them to eat, you can always add more as you need them. the best thing for doing a saltwater tank is to go slow and do as much research as possible.
as for adding more live rock, do not add it directly to your tank after you buy it! set up a tupperware with pre-mixed saltwater, powerhead(s) and a heater- keep the bucket/container at ideal conditions... SG, temp, water flow and put your rocks in there. let the rocks "cure" in the bucket BEFORE adding them to your tank. if you add live rock to an already cycled tank, most likely the new die off will start another cycle and kill your live stock