Preheating the water in a kettle mitigates the temperature concerns and variability mentioned in your first paragraph. For the Moka pot itself, medium heat on

Preheating the water in a kettle mitigates the temperature concerns and variability mentioned in your first paragraph. For the Moka pot itself, medium heat on a stove is a good place to start, but you can easily fine tune that based on what the flow looks like after one brew.