1) Ditch the deflector stone - no one, not even Dennis, uses it. Just slows down your cooks to heat up the extra mass. Just put some aluminum foil on the lower grate to serve as your heat deflector. You don't need mass, just a barrier to the infrared heat from the coals. Save the double bottom pan for its intended use - catching drippings onto veggies or making a nice gravy.
2) For that temp range, top vent should be about a 1/8 turn open (just barely off the seat) and the bottom vent is not controlling, just open enough to let air in for the fire. If you have the dual dial lower vent door, either: use one of the middle holes on the right, or a 1/4" sliver on the left one.