I used the flow rate discussed in the start up thread. I have a 55g 1300gph flow in my tank using 2 Koralia #1 and other filtration from my fuge. I really like the Koralia #1 it can barely flip sand 14" from it. I've built my first refuge just like you but since mine was a fuge only my design was much simplier. I plan to use something similar to your design to add a second 10g as a sump.
The only other thing I would advise you to get depending on surges is a battery backup for your Koralia pumps. I had a 2 hour power outage, ran my koralias on battery backup, and had no issues from it. I chose the smaller pump because they are only 4 watts fans for my battery backup.
I don't have any high water flow areas in my tank, but I don't have any corals that require more than a medium flow.
10. FLOW IS KEY IN KEEPING A HEALTHY TANK. Having adequate amounts of flow in your tank will largely determine how clean your tank stays. If you do not have enough flow to keep the water movement and to prevent dead spots, you will deal with algae issues, detritus and debris build-up, and nitrate issues. Shoot for at least 15 times the turnover of your tank volume per hour, but preferably, 20 times. This means that if you have a 55 gallon aquarium, you want to be turning it over 55 times 20, which equals 1100 gallons per hour coming from your filter, powerheads, skimmer, etc. Anyone with a larger tank or who does not like the look of powerheads should consider running a closed loop (which is very simple to set up).