Few overflow ?'s

Ok, setting up a 125 FOWLR. It will be linked into a 40 g sump/fuge. This sump will also be for my 55 as well.
Almost there on planning, just need to cover a few bases...
I will run out of the 55 using standard overflow box (external) Now i using a Rio 2100 for return. This will run into the sump about 4' over. Hard plunbing ok here, one 90* elbow? Or will it not be enough siphon with so many feet being used?
Ok for the 125, I figure I need a pump around 850-1200gph, it will also use an overflow box. Dual I believe, one going to skimmer chamber and one with valve to control a flow to refugium. Will this work? A control valve of some sort on the actual overflow pipe to restrict flow, or would the flow back up into he HOB overflow? I think it should work.
The 125's return will lead into spraybar.
So, am I right as to size of pump needed on the 125? Dual overflow box with one valve to restrict flow? Isn't the amount of overflow determiend by how large of pump oyu have for return? No probelms running two pumps like this? Need ot get one big pump to split both returns instead?
Am I making sense? I am confusing myself, someone help me out of this mess!
Thanks, any and all input appreciated!
S