Nice looking design. IMHO, I would put a tee and valve after the pump exit to the waterfall since you do not have to go through the filter. This way, you can turn it on or off and have full unrestricted flow. Use a Jandy valve that allows you to automate that valve if needed with an actuator, or as a minimum allows you to manual control the amount of flow to the waterfall. Also, the Jandy valve can be repaired easily in the future.
On your suction lines, I would also put Jandy 2 way valve on each of the skimmer and main drain suctions. This allows you to adjust the suction flow for each because 1 skimmer will likely be closer to the pump then the other and you can better balance the suction if needed. Also, the Jandy valves are repairable vs. the traditional PVC on/off valves (which need to be cut out to replace)
Definitely would consider the heater bypass mentioned earlier. You will need a valve and a check valve for this hookup.