Training fast-twitch muscles for Stepmania

[Arch0wl]

So I am interested in answering the following questions here:

(A) Assuming someone wanted to increase their finger-to-finger dexterity (e.g. ability to trill between ring and middle finger, or ring and pinky, or middle and pinky, and so on) how would they best do this?

(A.1) For (A), what is the ideal practice time? Should they "train to failure", and would more practice lead to more gains?

(A.2) For (A), would high protein / high calorie diets lead to more gains as they do in bodybuilding?

(A.3) For (A), would Stepmania players see greater speed gains by taking steroids? (This is a hypothetical, I do not advocate this.)

(B) Assuming someone wanted to increase their key-to-key dexterity (say, being able to go from getting an F on Disregard, index, to getting an A on disregard index), how would they best increase this kind of speed?

(Same questions applied to (A) apply to (B))

(C) If muscle fibers influence speed to a great extent, why don't more piano players and by extension Stepmania players have much larger forearms? Or is the "stepmania muscle" not visible?