I personally would not add any livestock to the tank yet. I have a system (2 weeks old) like yours that has never shown ammonia, nitritates and low nitrates. But, I am not moving the critters from my other tank to this one for a while yet just to be sure.

What I am doing though is getting the micro-fauna going really strong first. I'm getting the pods, stomatella, bristle worms, mysis and scuds to really breed. I want those critters good, strong and testing my system. Once I realize it can handle them, I know it will be ready for the "real" livestock.

If your itching to add something, I would add those micro-fauna and let them test out the system and add to the system. Those detrivores are invaluable to the health of your aquarium. And that carrib-sea live sand is good for your bacteria, but very low on the micro-fauna. I would ask/barter/buy sand from LFS and other reefers and that should boost your sand quite a lot.

While I haven't been on these boards for long, I've seen enough people outside of the board nuke their system from moving too quickly. I know you want those awesome corals and fish and inverts to look at.

You will NEVER regret going too slow, but you MAY regret going too fast.