So i finally read the entire three pages, I'm basically at the same point with my build thread as you. Miracles made my tank as well and I picked it up from there. They have a nice size shop ... Thick glass is so sexy!
Couple questions though, I see you have spent a large amount on various pumps and equipment, however those pumps will cost a fortune to run them all. I have to agree with aquatron, using 1 pump to feed a manifold is much more efficient. Perhaps using a true sine wave pump or controllable DC would be even more efficient offering silient operation, lots of power and low energy when compared to typical centrifugal pumps. I'm using 3 pumps total in my entire system, 2 for closed loop which is way more than i need and one for return.
Your return should only flow as much as your skimmer is rated for, having more flow makes the skimmer less efficient. Therefore the ideal flow through most sumps our size would be about 800 gph. Again this is dictated by your skimmer,
Your sump design is a good choice. Having all inputs at one end is far superior and a better use of space under the tank. Couple things I would look to add might include bubble trap for incoming water from DT, filter socks mounting area (i am working on adding a piece of acrylic to hang filter socks on mine. You don't have to use them often but when your cleaning and making a mess, they clear up the water pretty quickly. The rest of the space can be used for many other items, skimmer section, return section, DSB refugium or a water change chamber.
The fishroom looks very well done, I look forward to seeing it all come together. I noticed you bought the litermeter, to do automatic water changes, I was initially going to do the same but i don't think you will find it as the best use of a decent dosing pump. Send me a msg when you want to get into more detail with this and maybe I can help you. I'm in the middle of building a sweet prototype
Cheers
Rob