Some other things to consider. Check the power consumption of the pump you want to use. You might end up spending a pretty good chunk of change to run a large waterfall pump 24/7. Air pumps typically will aerate water for cheaper than water pumps. On the waterfall pump i would recommend pulling water from the other side of the pond from the water fall or a deep point on the pond to help insure proper mixing of the newly aerated water as it comes off the waterfall. You can also put a T in the suction line to draw from 2 or more points if you feel it's necessary. The easiest way to build a waterfall is probably to set a pond liner under it and stack the rocks on that to help insure minimal leakage. To avoid problems with your pump make sure you plumbing
Lines are properly sized, but as a general rule of thumb, bigger is better, especially on the suction side. Often times undersized or long suction runs will cause the pump to cabotage which makes them noisy and drastically shortens their working lifespan. Correctly sized or slightly oversized plumbing will contribute to you pump moving the maximum amount of water for the amount of energy used, by reducing the dynamic head pressure. Plumbing that is drastically oversized will can also reduce the efficiency of the system because the static head pressure is increased enough that it offsets the reduction in dynamic head. Also if you can try to use "sweep" 90s instead of the typical hard 90s of you can as this helps to allow water to flow more efficiently.
