I don't use Sketchbook, so I can't help you there, but to give you an example with Photoshop, it uses [ to decrease brush size and ] to increase it.
So in the Wacom setup utility, I select Photoshop for the App, the Touch Strips for the object, and since the touchstrips only differ from the touch ring in that they are straight lines while the ring is a circle, there are 2 settings for directions (up/down for strips, clockwise/counterclockwise for rings)
Set them to register a keystroke, [ to decrease brush size and ] to increase (or whatever Sketchbook uses)
Can't help you on your bonus Q, I myself am looking for good graphite brushes to emulate 4H 2B and other hardness/black pencils. Would like to get a nice repository of brushes like it too: charcoal, wax, crayon, pen, calligraphic pen, etc.
"Doing something half-assed more than once just makes you more of an ass."
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