Here is a link about the Nest thermostat and a dehumidifier. Your Nest model may work. Professional HVAC installers don't like to get involved with Nest thermostats. The sales guy will probably discourage you from connecting to the Nest and suggest installing a separate humidistat to control the dehumidifier.

Here is a video showing Ultra-Aire 98H installed with a Nest thermostat. This installation happens to be with a heat pump.

If the basement tends to have higher humidity, then it would make sense to install it on that system. If the humidity is about the same, then installing on the larger air handler is probably the best option.

You should ask how the dehumidifier is going to be integrated with the air handler, the model numbers of all equipment, and warranty information. You should get 2-3 quotes to compare how each company's proposed solution. Don't be pressured by the sales guy to sign up until you understand everything.

Thank you Mike. I'm still trying to figure out what generation my Nest is. It says model: backplate 5.4. The serial number starts with 09DA02. I see information about 1st and 2nd and what their serial numbers start with and they don't match mine. I'm thinking maybe I have 3rd generation??

Right now the AC is set at 69. My daylight basement is 47% and my main level is 43% but hasn't gone on yet because outside temp is 69.

Here is a link: How to tell which Nest Thermostat I have You can also call the Google Nest help line.

I think I figured out I have the 3rd generation Nest. HVAC sales guy didn't show up. Guess I have some time to look into this more.