If I did something like this can I just place the shaped cake on top of the sheet cake or will it be too heavy and crack? How would I cut it?  TIA :-)

I, personally play it safe. Haven,t done one like this before. But , I would have the hat cake on same shape cake board as cake. I would place a few plastic dowels on bottom cake, and center dowel thru the hat cake. This way, you won,t be worried as you pick it up or travel with it(or client travel with it) that it will split and fall apart. This is just how I would do it. Im sure  you will get more responses.YOu could take off hat cake or leave on and cut that first, etc.. I forgot , I have done a over the hill cake like this, or a soccer ball cake, one time. I just like to be sure. hth

I have done something similar with a cake which was two levels and I cut some thick board and covered in aluminium foil to the shape.  I then got some of those larger type drinking straws and cut a lot of them up to support the weight - I found it easier than cutting dowels and if you get them in straight and enough of them they will take the weight.

Is that a single 2"- deep layer cake on a single 2"- deep layer sheet cake.

It looks like one of the Wilton cake pans and although it has a shape, it is shaped only as to the perimeter and it is not stacked-and-carved or tall.

When I had Wilton shaped character pans I used to put one on a sheet cake.  It's just a normal layer cake. IMO