You'll need at least 4 per stack, one for each corner, although you can print 6 if you want more stability. I would recommend a high infill as well, otherwise you may experience some “droop” if using heavier sheets.
My initial design used large-size 3M command strips, but these started to wear out after several months of having load on them, so I swapped to a design with a hole for a screw.
For my case, I'm using the baking sheets that came with my Toshiba steam oven, but I imagine similar style oven sheets will also fit from other brands (Hitachi, Panasonic, Sharp, etc.). I attached the .step files to allow anyone to modify to fit the thickness of their own sheets.
Be careful of the tolerances/ gaps when installing these, as if they are too far apart then the oven sheets may either slip out, or they will wear out too quickly if the sheet is just balanced on the edge of the lip rather then pushed in all the way.
The author marked this model as their own original creation.