Sump Question: Eshopps RS-200

Here is the sump I'm thinking about buying.

Eshopps RS-200 Sump:
Reef Aquarium Filtration: Eshopps Reef Sumps

First of all I have a 125 gallon tank with a Eshopps PF-800 overflow box and a mag 9.5 return pump.

I'm newb on sumps, really am, but I have the basic idea. I just want to know how this specific sump works, let me know if I'm wrong or right. This micron bag is really throwin me off though. Do I put something in like bioballs in the bag or just let it sit? I'm confused ...

Also in the first section... Is this were I should put some live sand and some live rock with the protein skimmer all in the same area??

I'm assuming the sponge and the two dividers are for micro bubbles. Then the last section is were I put my return pump so water can flow back into the display tank.

Do I have the right idea for this setup? If not, please correct me. This sump looks cool and I already have the overflow+return pump that would be fine for this.

Let me know what you guys think. Thanks!!;D

 

you've got the idea.