I got a filter sock with my sump and used it for a couple months.. but turned out to be just another thing that turns into a pain in the *** because it does get clogged up and for me, it caused an overflow problem. I just switched to using different micron filter pads in my first chamber and haven't had a problem since.
I do know a lot of vet reefers that do use the socks though. If you can deal with constant cleaning of it then I am sure it works good.. I just got tired of doing that when I can cut a new piece of filter and change it out a lot faster than washing the sock.
So... why did you decide to make your sump the way you did? I don't think it is wrong, it's just that I have never seen one built like yours.. the first "return" chamber anyway. You saw my pic.. the water goes down, through all the filters/media then into the next chamber.. it doesn't go in and up/over through the holes like yours. I am sure you did a ton of research on it so I wanted to pick your brain on what the reasoning was.
Edit: Actually, it may work A LOT better if you put in just one more baffle from the very top of the sump to about 2" from the bottom in that first chamber. Leave about 1" gap before the baffle with the holes, that way, the return water goes into the first chamber, then it has to go down to be able to go back up through the holes. Then you can put in filter pad/carbon/etc in that chamber and have the water flow through it. Just a suggestion.