Medium heat

It's all relative. Depends on your stove, your pan, how long you preheated your pan, etc. I think you just have to cook with your new pan until you get the hang of it.

Depending on your pan, if it has an aluminum layer, it will disperse heat more evenly and quickly than anything else u might have used. So medium for a pan like this would be more like between low and medium on you stove knob. When you get into higher end nicer cook where you should never have to cook with your heat higher than medium on your stove top

Depending on what type of oil you're using, I would probably go for number 3 to 4, or just under half way on your knob.