Why no check valve on the return? IMO they're a great piece of mind especially if you like to keep your sump filled to the max.
Also, you don't plan on putting the bioballs back in do you? And if you could, it would probably be better to put the skimmer somewhere in the middle portion if it's possible, maybe hang it from the back of the sump
No the bioball are out for good. I can probably put the skimmer in the middle chamber but I was considering using that section for a future refuge.