What should I get to control my dehumidifier?

You might check the thread below. I’d just use the humidity sensor in the ecobee. Aeon Multi 6 motion sensors also have a reasonably decent humidity sensor. Then, you can use SmartLighting or WebCoRE to turn the dehumidifier on or off. I have my dehumidifier on a plug using a WebCoRE piston. The thread will have examples and thoughts: