still awaiting my decal to put on the case.. but yeah a thinner sticker/decal (well normal thickness) will be fine. an invisible shield fits behind it and that has a bit of thickness.
as for a size cutout, as user mentioned above, use the white paper that fits into the case that comes with the case.
as for a size cutout, as user mentioned above, use the white paper that fits into the case that comes with the case.