I would use either 1 or 2, 2" drains with a calfo style overflow. If you build a stand to contain the sump, the falling water will be less noticible. I say use 2" just in case a turbo snail decides to take a trip down, it won't stop the flow of water. Use duro styled pipes (basically a T fitting coming off your bulkhead) and put a cap on the top with a hole drilled into it to allow air in the tube which will stop the gurgling. I figure if you slanted the over flow it would be more quiet. By slanting, I mean taking the overflow box, and the main piece, should stick out further at the surface then it does at it's base. That way water does not spill over into the overflow box, it would gently glide over the edge and into the box. Also, a small return pump like a mag7 should help keep it quiet and provide enough turnover for your application. If you don't want powerheads, you could add a SWCD. If you do add a SWCD, you may want to notch up to a mag9 or 12 to provide enough flow without powerheads. The new style SWCDs are much more reliable and do not have the tendency to stick as much anymore. Otherwise, you may need to craft a return system with some PVC and drill holes.