Setting Brush size by % is'nt tablet friendly at all. (slower the workflow)
it need to be a slider, please.

I wish the color picker were more accessible, not a tool, but a floating palette
or a shortcuts to easily switch between Brush and color picker.
Alt is a common shortcut for this tool, returning to brush when alt not pressed.

you have the best oil brush avaliable.
Keep up the good work.