Sounds like we have the same house plans. I just had some duct updates done to my system when we replaced it and ran a new trunk up to the attic to push more air up there. The other upgrade was adding a large air return downstairs to help move the air from top to bottom, has made a huge difference, is almost consistent upstairs as with the down. Might take a look to see what your air return to duct ratio is and make sure the system is moving the air it needs to. I only had two air returns in the whole house and both were upstairs, the HVAC was starving for more air to circulate.
Part A sounds like it will work, though just adding more cellulose on top would also work, just be sure your ridge vents don't get clogged in either case and air can circulate up into your attic and you have adequate ridge or gable vents for the air to draw out of the attic, both for moisture and heat build-up reasons.
Part B, I think I'd find the wider rolls of insulation that they use for wrapping ducts or in morton buildings to hang over the knee walls, it's probably got as good of an R value and could put a slice in the foil side to let it breath if you're concerned about the moisture barrier.
To a small child, the perfect granddad is unafraid of big dogs and fierce storms but absolutely terrified of the word “boo.” – Robert Brault