Hello and welcome (back) to the saltwater hobby!
I'm a gear junkie myself and I think backstage is half the fun with keeping a reef tank 😊👍
Maybe my suggestions on sump is too little too late, but here it comes anyway.
Your filter sock holder seems to be the lid of your refugium. A filter sock, depending on micron, flow and bioload in the system would probably need to be changed/cleaned every 3-5 days. After that it's to thick on debris that water can't go through. This will lead the sock to "overflow", and if I have understood your setup correctly this will means thst water will flow over the lid and pass by your refugium chamber? If so, that would probably render your biological filter useless - until you clean your filter sock. Until then two of your" export" filters might be reduced or have no effect.
I would say that mechanical filter (sock) is good, but it's not essential. I've seen many use the macro algea as both biological and mechanical filter. You will get some debris stuck in the green hairball that otherwise would have stayed put in the filter sock, but you also do harvest (throw) macro algea from time to time anyway, which also removes any debris stuck in that harvested algea.
I myself have removed my roller filter and see no change in nutrients (bare in mind my system has been running for a while).
To get a few extra square cm of refugium I would probably skip the small water passageway after the refugium. See my Picasso art in the attached picture.
agree with kaptenen, that a comb all the way is good, but I see no use in forcing the water to go through at the bottom. But I might of course have missed a function with that?
EDIT: I see that this section is not in your last sketch, so maybe nevermind this part in my input 😊
I agree with many others that live rock is the way to go. If the reason to get dry rock is to avoid any pests or hitchhikers, that means that you would need to have some pretty serious quarantine process for every little piece of frag or fish that you introduce onwards. Otherwise dry rock, for that purpose, would be like cleaning your car on a muddy day in February 😊 not quite worth the while.