YMMV, but one of our stores is 400x200x35 with 10 foot shelves, and we can light it up with as few as 5 AP93 with some issues near the floor between the shelves and poor coverage in the freezers.
When we went to 10 AP93, all complaints vanished.
I'd predict that you need as few as 10, but would recommend you plan for full shelves and do an actuall survey at some point.
--Matthew