Mbwaldrp

If you the homeowner want to independently control humidity setting in AC cooling, then the preferred thermostat is Honeywell Vision Pro IAQ that has "dehumidify on demand" feature. With this stat, comfort r setting is disabled.

Second choice would be Trane or AmStd 803 or identical HW 8321 that
makes the Trane stat. Comfort R setting is used with this stat.

Before I made any changes, you need to take some humidity readings at several different areas in your home at different times of the day.

There are too many variables to make a good and accurate answer to your final question. I will say this. If you don't have zoning controls for controlling temperature Between first and second floor, you can expect a temperature differential of up to 10 degrees. This can depend on ductwork design/sizing, insulation/building qualities,whether you have damper control between airflow to first/second floor, and where the thermostat is
located.

IMO

IMO