Here is the link to the serving chart sizes you can decide what you want from that.
If you do a 12, 9, 6 that will give you 100 with a double layer 2 inch pan. That would be if you want to serve the top tier. If you don't serve the top, I would do a 14, 10, 6 which would give you 116 servings plus the top.
That cake looks like it has atleast 3 inches difference on layers.
I agree 14, 10, 6 = 116. They can choose to serve the top 6"er or not. This is based on serving slices 1x2x4.
Be sure you get a board that is at least 20" so you have room for those roses at the bottom.
thanks so much for getting back to me... i am still learning and the help I get from CC is wonderful!!!!