The reflector method with the skillet I have yet to try, but may on friday at Rock Creek Station, my slow day and set up day, we'll see.
As for in the dutch oven about 1/3 of the coals on bottom, 2/3rds on top and enough to get the oven to about 375-450. this, depending on the wood should pretty well fill the lid but not be really heaped and about 1/2 as much on the bottom. Check them and check them often till you get the hang of it.
I check my temps by touching the side of the oven,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,real quickly.