Minimum Draft

That will depend on your ash buildup. Many factory smokers have 1 1/2 to 2 inches and can get full of ash before you are done with your cook, causing the fire to starve for oxygen. When I made the grate for the fire box in my BSKD I think it was about 3 1/2 inches. Not sure, that was awhile ago. I burn pretty much all wood with no charcoal, and depending on the species of wood, that can create a lot of ash.

Just off the top of my head I'd say four inches, pufferbelly. On a long cook you can fill half that up easily, still leaving enough room for some air.

My Lang 84 has about 6 inches

What size cooker/firebox?

A big stick burner that eats logs will need more air space than a small charcoal burner. Also depends on how often you're willing/able to clean the ash out. I have to "sweep" my NBBD about 3 times during an all-day cook like a 12 hour brisket. My grate sits about 3-4 inches from the firebox floor; but I've also cooked without a grate and with it raised about 5-6 inches depending on the length of cook, size of fuel and heat of fire I want, etc.

More confused yet?