Do I just connect thermal pads to the ground plane and call it a day?
Yup.
Wouldn’t that make the components hard to solder with hot air?
Sorry, I’ve never tried hot air assembly.
Do I make an isolated polygon that only acts as a thermal pad?
Ideally the copper area is big to spread out the heat. If you have an isolated polygon it can’t spread very far and buys you less cooling.
I was expecting Hal