If you're going to put Cheato in the sump, then you need a light down there.
You can find Cheato at SW
specialty shops or online vendors. It removes nitrates and other organics from the water as it grows. You have to prune the Cheato occasionally to permenantly remove the organics from the system. Cheato and other macro algaes are good for reducing your nitrates beoynd what the skimmer and water changes can do alone. This is optional until you start trying to keep very sensitive corals.
Live rock rubble is a good place for pods
to breed. Pods
will A) eat a few nutritents in the system, and B) be food for corals. You don't have to put a light over the rubble for this to work, although there will be a greater variety of pods
produced if you do.