I have finished the enemy sprites and the enemy placement for Stage 1 today. I also completed, after days of work, the song that plays in this stage, although I am not entirely sure if maybe I will put it somewhere else.
As for the music in general, it will be a mix of modern electronic beats and classical score. The music will be written mostly by myself. Wolfgang Schall (http://www.playsmallgames.de/) composed two tracks which I re-arranged myself.