Higher the better for the Pond Pump. I think you have a type, should be 250 gph. I have one that is 550 gph, and I find that I want more flow, as the cooling rate would be higher. This is with a 50 ft 1/2 inch copper chiller.
Use tap water to get down to <100F, then hook up the pond pump (might be yoiur plan). This time of year I do not need the ice bath/pond pump for ales. Do need it for lagers. Did a 10 gallon batch of Pils yesterday, and it required 2x7 lb bags of ice to get from 66 to 46 F.