#1
hey UG,
its probably a stupid question, but if u adjust the action on a guitar does that mean that u would have to reset the pickup height
#3
Since pickup height is more reliant on personal preference (a few would argue against that) then no. You'll only have to change the pickup height if you think it made a difference in your tone.

Edit: beaten to it.
#4
yeh but if u raise the action is gonna be higher at the bridge pickup than it would be at the neck pickup. So it would be on a slant (depending on the nut height) which would probably chance the volume balance between the bridge and neck
#5
still prefrence, who know's maybe you want a volume differnce, so you can switch to one to do one technique that is harder to do loud, and just hitting the pick-up switch is easier then a volume knob or pedal. You can find a use for anything, even if it's not one you would use it for.