I think it's better to do various elements of music separately and combine them rather than try to do the whole song at once. It's a challenging problem. There is much less training data for example. I've worked on melodies so far: https://www.melodies.ai/, https://www.youtube.com/playlist?list=PLoCzMRqh5SkFPG0-RIAR8jYRaICWubUdx.