To add experience to what I wrote as a plan a year ago.
The WI-FI controllers work fine.
I bought 4-pack of them on amazon and they come to about $10 a piece, so cheap enough. Use them for pool lights as well.
For humidifier control, I install automotive relay on its sensor wire and 12V charger (from old answering machine) plug into WI-FI controller.
Purge valve has its own charger, that I directly plug into WI-FI controller.
So my set for the humidifier is to start water purge 1 hr before humidifier starts. Factory set gives purge about 8 seconds with intervals every 20 minutes.
I did not like the idea about purging boiling water and having softener - purging is not high priority.
So resetting purge to 20 seconds and turning the WI-FI switch for 1/2 hr early in the morning -gives it double purge, what I believe replace over 90% of water in cold humidifier.
Than 2nd WI-FI plug starts humidifier 1/2 hr before furnace starts morning cycle.
This way I maximize fan use when furnace and humidifier runs together.
The main schedule runs humidifier for 4 hr in the morning and I set the sensor to 30%. (took some try by error as there is no numeric scale on factory dial).
This way the system gives me 30% humidity in the morning and on extreme days I use my android to give it more time for additional humidifying.
Hope it is clear enough?