You should have a timer for this tank and it should have a consistent 12 hours of light. You may have to alter depending on algae growth.
What type of bulb/s came with nanocube?
Do you have a test kit and hydrometer? You will have to keep on top of evaporation.
Let your tank sit for a couple of weeks before you get any livestock. Tank needs to cycle.
After it cycles, you should limit yourself to one fish, 2 inches. Clown gobies are colorful and interesting. Check out www.liveaquaria.com
they have a nano fish section in there salt water fish section to give you ideas.
You'll also be able to add a couple of hermit crabs and snails.