Insulating Cape Cod Attic

I'm redoing a Cape Cod attic I just purchased. I'm gutting it because it has mold due to little to none ventilation or air sealing and little but poorly done insulation.

For the knee wall I'm thinking drywall on conditioned side with R-13 fiberglass in cavity and 1" ridged foam on attic side. All sealed up. For slant (2x6) drywall with 4" ridged foam and a 2' gap by roof for ventilation. Ceiling I will add 2 x 4 collar ties that will be drywalled with faced R-13 fiberglass and then unfaced R-30 on top perpendicular. There already is a ridge vent and two gable vents up. Will add soffit vents below.

~ Do I need to close off the gable vents? I've read they can interfere with the flow from the soffit to ridge vents.

~ What is best way to air seal electrical boxes in the kneewall and attic floor (from ceiling on 1st floor)? Spray foam around the back of box?

The two end walls are already drywalled with R-11 fiberglass inside. Should I tear it down, re-insulated with R-13 and put up new drywall? Doesn't seem it would be worth the trouble. Do I need any sealing on top of those walls above the ceiling line?

~ Should I add any radiant barriers?

THANKS for any input.

Insulating Cape Cod Attic