Re pump size, not only does the pump 'size', flowrate, depend on the size of the pond and the fish load etc, it also depends on how 'high' you want to lift the water and through what plumbing the water is pushed. Plus if you want visual effects eg a stream and/or a water fall the requirements of that may warrent a bigger pump than the filration minimum.
My pond is about 1350UK gal, my stream takes about 1633UK gph from an aquamax 10,000.
When choosing a pump you really need to define the actual lift and estimate the friction-losses/pipe-loss in the plumbing etc, then add these two to get the total "head" that the pump will have to overcome. Then look at flow charts for various pumps and see which will meet your needs.