I have never done a stacked cake before and for my niece's upcoming B- Day, I am making her a mad hatter cake w/ Alice on top of the hat.  I was going to stack 2,   10 inch cakes on the bottom, 2  2 , 11 inch cakes for the middle  and 2, 12 inch cakes for the  top layer of the hat.   Ea ch individual cake will be 2 inches for a total of a 6 inch hat(give or take depending on icing and fondant).   Alice was going to be a dome cake for the dress and Barbie sticking out of the top and will sit on top of the 12 inch top layer.   I was going to use a  10 inch round separator plate  with short egs stuck in the cake between the 11 and 12 inch ayer   and an 8 inch separator plate between the 10 and 11 inch layer.  Does my description make any sense?  Do I need any dowels or any other support if the layers are resting on the plates?

It makes sense to me. I assume you'll be carving away the extra cake that's hanging over to get the hat shape that is large at the top and smaller at the bottom.

You didn't mention using support legs anywhere but in the middle. Don't forget to use the legs on your 8" plate that goes into your 10" base tier. Also, I'd use supports in your top 12" tier before you place the dome tier on the top for the Alice "Barbie" dress. Good luck!