Regarding the Koralias and the on/off cycles...
If you're running the newer Koralia "Evo" series, those can be cycled on and off repeatedly without damaging the powerheads or shortening their life span.
However, if you're running the older Koralias, you will definitely shorten their lifespan if you switch them on and off like a wavemaker. If you're not looking for variable flow and just want an on/off cycle, the new "Evo" Koralias are a fairly low cost option.