I'm starting a topsy turvey cake tomorrow and just need to know should each cake be 2 or 3 layers of cake? I'm doing a 3 tier.

I think everyone does it differently. I use two layers of cake and then I carve the angle, then flip the carved piece upside down and stick it back on the cake with icing to make a greater angle and keep the servings.

If you don't plan on using the cut part back on the top of the tier, then you will want to bake three layers, and carve (I have a friend who does it that way.), and plus your tiers will be slightly taller that way as well.