You can make the gold stars & eagle topper at least 3 weeks in advance which will make the final assembly a snap. I would say that the majority of people own a 8" cake pan but if you are using a box mix this doesn't make for a tall cake. To create a tall cake without the waste, bake your mix in a 6" pan that is 3" tall, you can divide that into 3 pieces once filled it should be 4" tall. Here is a blog post which explains how to torte a cake.
Once I had filled and covered my cake in white buttercream I put it in the freezer. The actual decorating process was very fast since I had made my decorations in advance, once done I put the completely decorated frozen cake back in the freezer to be enjoyed at a later time.
Here are all the piping tips I used to create the buttercream borders.
Here is the template for the eagle topper:
Assorted supplies used for this project