I've just been viewing a video of Olivier Latry at Notre Dame playing the Passacaglia and Fugue in C minor by Bach.
https://www.youtube.com/watch?v=NRVG42lGUkYHis registrations are all managed using the stepper. There's an abundance of pedalboard views throughout the video, and it would appear that there are two stepper advance toe studs - one on each side of the swell pedals. Mostly he presses the one on the right, but there are times where it is clear that he's using the one on the left. There's at least one moment I can recall where he actually uses the right foot on the left toe stud while the left foot is playing low down on the pedalboard. This makes sense, because by keeping the knees together the right leg is already pivoted towards the left. Reaching for a sequencer advance toe stud to the right of the swell shoes at that moment would have involved a greater stretch, but going for the one on the left with the right foot is neater and involves less physical movement. Having an advance toe stud on the left also makes it easier to use the left foot on the toe stud if the right foot is busy on the pedal keys at that moment.
Duplication of the stepper advance on both sides of the swells makes sense to me. I am planning some changes which will involve relocation of the toe studs plus installation of new swell shoes on my console. At present I have the stepper toe stud as the first one immediately to the right of the crescendo pedal and I intend to keep this. The idea of duplicating it on the other side is something which I am now considering. I already have stepper thumb pistons on both sides of the piston rails on all the manuals - flanking the divisional pistons - so the idea of doing the same with the toe studs is appealing.
Meanwhile, as has already been noted, the page turn could reasonably be put anywhere else for convenience. I am considering adding a page turn piston even though at this stage I don't use a digital music display, but perhaps one day I will.
Andrew