I'm making a 2 tiered cake for my nice but she doesn't like my fondant and wants butter cream instead. I have never done a cake in only butter cream, how do i make it smooth and how do i add the detail (she wants a music scale around the bottom)? I could use any tips/advise.

Use a crusting buttercream. Wait until it crusts and then smooth it with a Viva paper towel. Viva is the only one without a pattern on it. I lay a viva towel on it and then roll over it with a small 6" rolling pin. Let it crust up very well and then add your design with a stencil and some thinned out buttercream or royal icing. You want it thin enough to smooth out but not thin enough to run. Hope this helps.