I think you need a bubble trap between the fuge and return chamber.
Is it your intention t have all 3 chambers be around the same height?
Have you considered dumping one of the drains directly into the fuge and not having the T which will impact your return pressure, plus the split to the manifold will reduce it further.
Final thought, I just designed a new sump and after 5 revisions I figured out my chambers were a little tight form my equipment and I had to make a lot of changes, make sure you have access space, i.e.you can get the skimmer in and out of the sump once you have it in the stand. I bought a setup 2 years ago and the only way I could get the skimmer in and out was to remove the plumbing and take the sump out and then the reverse. My new tank I can remove everything at any time, including swapping out the return pump.
I posted my designs here and got some great feedback.