Here is my hydraulic plan for comment. Unlike the architecture, where I don't have too much room to move at this stage, I am very open to suggestion here. I will try to capture US Gallon and feet units on this drawing tonight. Blue shaded area is inside house.
I have observed the following principles.
1) Everything must have built in redundancy. The circulation system of an aquarium is like our heart & lungs... failure results in catastrophe pretty quickly.
2) Must use the lowest possible energy. I am not very happy that I can't gravity feed the skimmer from the main tank, but I have too little head.
If anyone is wondering why I have gone with 4" drain from the main tank to the sump, it is because I have to move 7000 Gal/hr 100 horizontal feet with only 3.5' head. Requires fat pipe. The reason I have 2 of them is so that I can switch active pipes for cleaning (i.e. soaking in vinegar for a couple of days). When you are running pipe through concrete foundations, you have to plan for a means of cleaning that does not involve tearing the house down.
The pump brand I have selected (Finish Thompson DB series) are magnetic drive and very high quality. They also have a very broad selection of operating points (flow & head).
"Filter" under the quarantine tanks is actually a combination of UV & ozone.