The biggest problem with a sump that small is ensuring that you have a sufficient bubble trap otherwise you'll get micro bubbles in your return lines.
I have the same thing on a 10 gallon. I actually use 2 ten gallons on my 72 bow, as dictated by my area in and under my stand. I use 1 ten gallon for the sump and one 10 gallon for the refuge.
For a poor man's bubble trap design I just used a 5 gallon plastic waste container from Home Depot, cut to the size I want for level in the tank. Then I drilled a bunch of 3/8" holes all the way around it. I used 1/2 PVC and egg crate fastened by zip-ties to hold a carbon pad and collect the water from the tank, which runs through the pad then out the bottom where the holes are drilled.
2nd. I would make sure on your supply and return you put a shut off valve, which you can also use for balancing the return flow....supply from the tank is always 100% open. You can even get check valves from some online sources too, which I think I'll add someday.
I basically T- off the supply to the fuge with another shut off valve to balance the flow. Then the return from the fuge I just built my own U-Tube out of 1" PVC and fittings, drilled it an attached a suction line in the middle. The supply end of the tube I used a cap and drilled it out as much as the flow I wanted through the U-Tube.
