I learned a lot from this cake.
For one, rolled buttercream is harder to work with than fondant. The RB is much softer than fondant, and therefore has a tendency to tear under the weight of itself when you spread it over a cake, rather than stretching lightly like fondant does. A recommendation I read online after suggests making a 25:75 rolled buttercream to fondant mixture for best results.
For two, rolled buttercream is much shinier than fondant, so this must be taken into consideration in the design. Shine, or no shine, pick your preference. I found a few of my fingerprints stayed pressed into the cake.
For three, rolled buttercream, at least the chocolate variety than I can speak of, was a smash hit! Not everyone likes the taste of fondant but this rolled buttercream is a clear winner in my experience. You don't need a lot, either. A little goes a long way.
From the assembly angle, I learned that using impression mats on very soft surfaces (rolled buttercream versus fondant) can make cleanup a pain because small pieces of the buttercream got lodged in the holes in the letters saying "happy birthday". Those little 'a', 'p', 'b' and 'd' holes required toothpicks to clean 'em out.
I learned also that I should have had more practice piping zigzags. It's been a while, and I'm a little rusty, apparently. But, in the end, a well received cake makes me a happy baker, and that's enough for me.