wow! This sounds like a really large cake....you are definitely going to have to have a board for every 2 layers you have.... This would end up being like a 12-14" cake!
you are definitely going to need a center dowel and I am thinking you would use round style cake instead of square.
I think you are going to have to do this topsy turvy style. Like the style cakes with the wedges in it instead of the whole cake being at a slant by carving it. I don't know how to explain it or where to go from there...yes, I too am thinking that you should PM Doug. He is the MASTER at construction!
this sounds like a very large under taking! Good luck and please let us know how it goes! Direct Doug to the thread so that we can all see his idea!