you don't NEED to do anything...BioCubes are created as all in one systems.

With that said... you may WANT to run a skimmer depending on your plans with the system.

Water test your tank with some freshwater....turn the light on...does it cover the section you plan to use as a refugium? Yes, then it may work. But another nice option on the fuge is to have a reverse cycle...this helps maintain a constant PH. The fuge light would run on an opposite light cycle from the main light.

I would slow down on the buying part and spend some time researching the basics to keep a tank running. Then spend some time comparing mods done to this system by other reefers then decide what will work best for you before you buy anything else.

You may decide that you don't even want a skimmer or maybe you'll get crazy and hook up a sump and toss some cash at some LEDs lol.

Lots of options. Start with what you plan to keep first then allow that to determine how you want to run the system and what equipment you still need.