Thanks everyone! Had forgotten about a Tutti piston, and of course thought of the Pedal couplers
after I'd posted the question.
Appreciate the other ideas and links too.
So, speaking of coupler pistons - under which keyboard would you put them: the one you are playing and adding to; or the one you are adding?
For instance, Choir to Great - would it better to have it under the Great (since you're probably playing the Great when you need to add the Choir), or keep it under the Choir to associate which Division you are adding? I suspect the first option makes the most sense.
Then the Division to Pedal pistons - would they make more sense under their respective Divisions (ie. Choir to Pedal under the Choir)? Or should they be all in one place together, for instance under the middle keyboard to split the difference between all three, or under the lowest keyboard to be closest to the Pedals?
Thanks again!