I love this idea! Personally, I'd try any of the steps so long as it os like 6in wide at least. They must be pretty wide imo to be practical. As for the height, I'm inclined to try the step at the top of the rock rail.
I dont have a Bronco yet, but I know that the MGV does not come with rear armrest/cupholders. No, I dont know why the leather trim gets this but MGV doesnt.