I think a waterfall into a pond would be asthetically beautiful. Depending on how high the water has to be pumped will be one factor in determining how many GPH your pump will be. I'll let the experts chime in on how effective surface aeration is vs. diffusers on the bottom. I will say this, I'd hire a professional to build the water feature. Its a little more than placing some rocks on a slope and turning on the water. They aren't cheap, but my small waterfall turned out great. I'll look for a photo.
