Sorry I don't have any advice but I do have to say *
WOW
Now that I look at it I do have a couple concerns, *first you are pumping water out of the overflow? *If you are doing that you will need different size pumps because on the 7' head. *Is there a reason you want to use a pump because you could use a siphon.
I am not sure why you want to use a surge tank I think you would be better of using a pump in the upper refuge.
One last thing I like using PVC in any place you shouldn't have to take apart. The vinyl tubing is easier to dismantle if need be. Also any bends in you PVC will reduce your water flow, tubing won't do that unless it is kinked.
