Yes this is more or less as I thought myself:
Place a circulation/feeding pump in the back left corner of the middle chamber, use a fleksible tubing through the spare pipe in the same corner, from there through the grey inlet connection in the refugium to the bottom.
Outlet pipe connected with some PVC parts including a reduction from 32 to 20 mm to the spare pipe above the return chamber, or with less reduction through the open 30 mm hole in back corner of return chamber.
That means that water entering this feeding pump to refugium will not enter the skimmer.
In other words, maybe the flowthrough should be somewhat limited?
You suggest the Red Dragon® 5 ECO pump 25 Watt. As the sparepipe is narrow only 20 mm, any idea on optimum flow?
Any suggestion on wich parts you would use to make the flow line from the outlet piping?
As mentioned the refugium will only include Chaetos, so a decent flow and some kind of lights are what I think I need.