The top layer of cake that will have the cardboard support on top will be "naked," yes? In other words, there won't be any icing on it? Or is there a way for me to put icing on it, tape parchment paper to the cardboard round in order to keep the icing from sticking too much and then put my last cake on top of that? I just don't want the poor thing to be without icing when the cardboard comes off.

Ice the layer, tape wax paper to your board and spray it lightly with non-stick spray. Don't completely coat it or you may have slippage, just lightly coat and it should be fine. You can also put coconut or a bit of powdered sugar on top of the icing so the board does not stick.