That is a really tight space and I see that you are trying to keep the step out of the way so it doesn't interfere with all the doors in this area. My concern would be that the step is tucked in under the filler and will be a bit awkward to use. It looks like the height you have chosen is about the same height as the bottom of the hanging locker door. You could put a small step under the door fastened to the frame of the hanging locker door. It looks like you have about 2" ~ 3" clearance with the filler piece door open and from the slope of the floor it doesn't look like the head door swings all the way open (unless there is a cutout in the door not seen in these pictures.

If you want the step to be a bit wider you could mount it on a hinge under the hanging locker door and mount a wedge on the filler cabinet door that goes under the step and lifts it up out of the way when you open the cabinet door. That way there will never be a step left folded down that jams into your nice cabinets when opening a door.