Replacing R7 in exterior home walls
The black is dust that is deposited by air leaks.

The best building framework is passive house and the perfect wall which orders your priorities.   The first is liquid water, the seconds is air, the third is vapor and the last is insulation.

If you've gone to the trouble to open all the exterior walls to increase your insulation, I am going to assume that budget isn't the top priority.

I'd get aerobarrier to give you a quote for air sealing.  https://aerobarrier.net

Once it was airsealed.  I'd go with roxul for insulation.  A passive house membrane like intello on the warm side of the insulation for moisture barrier.  Then drywall like normal.

Big project, good luck !