This is my first large 3-4 tiered cake and I'm a little nervous. I have made smaller tiered cakes with success, but I'm making a large graduation cake for a gift & I want it to be great. .

I'm not sure what sizes the tiers should be. It needs to serve 150 people. I was thinking 16, 12, 8 & then a small graduation cap cake at the top, but any advice is welcome. (Have been studying up and practicing cake construction so that it will be stable and won't fall over.) 

Are these tier sizes good? Is there any special trick on how to torte a large cake layers?

Sorry if these questions seem silly. I'm a newbie to the boards! THANKS