Depending where you live (warm or cool) you might want 2 stage furnace and 1 stage ac. We run the heat from Oct-March and only the AC in more like Jun-August...so we it makes sense to get 2 stage heat instead of ac. I sprung for it and got both, 2-stage ac and 2-stage furnace.

A 2-stage AC will work best with a variable speed furnace. The variable blower would be able to adjust to the proper air flow to give the best comfort and humidity control.

There a 2-stage furnaces which are not variable speed. They operate a several fixed speeds. These can also work with 2-stage AC condensers, but it is a compromise on comfort and efficiency. These furnaces are cheaper since they do not have a variable speed blower.

I don't think any single stage furnace is set up to work with a 2-stage AC. I am suspect of any contractor who would propose this.