Chris, you certainly started a conversation.
I had a 30 gal
with a hob
skimmer/refugium very similar to the one you are designing. If a true sump is out of the question , as it was for me, then I only see 1 critical flaw in the design. If your return pump fails (power outage) you have very little volume before your sump overflows. I would raise the whole sump system so the top of the sump is at or very slightly above your DT waterline. Under normal operation you sump water level would still be below the tank level for a normal syphon.