Dr. Bran
Smash Apprentice
I can't say that I know of any exact tutorials on Smash-style games in GM, but I'm sure that videos or forums exist on the subject. Also, I wouldn't think about assets like music right now, because that can be added much later. Right now, start small. Start building the simplest version of the game that you possibly can and then build and tweak it from there. The simplest thing I can think of is a rectangle that can be moved across a big rectangle that resets when you fall off said rectangle. From there, you can experiment with attacks and stage collisions and all that jazz. Just don't get frustrated and give up! I really want to see what you do with this idea!