Split each of the three 8" chocolate cakes into two layers 3/4" tall.
Using a 1/4" wide tip, pipe 6 oz of ganache onto the first layer of cake and refrigerate until firm. Spread with warmed caramel sauce and top with 1/4 cup of chopped peanuts. Repeat with remaining cake layers. The top layer of cake gets only ganache and no caramel or peanuts. It can then be decorated with a cocoa powder stencil.
Speed up the process by piping the ganache onto all the cake layers at once and storing them separately in the refrigerator for up to a day. This way the ganache won't get too firm in between layers and you won't have to warm the caramel in the microwave as often. Then make sure the towering confection tastes as great as it looks by having your caterer store it in a well-air-conditioned room until right before serving.