Thanks for sharing your implementation! It's a lot simpler than I expected, it feels pretty complex. Very nice!
I'm right there with you on spending too long on the song, I made a rhythm game and took 2 days on mine. I couldn't move forward with other features until I had a song in, but I was really stuck on it. Turned out just fine, but I lost a lot of time to it... I learned a lot about Western musical tropes, though.
I look forward to seeing what you make out of the pile mechanic!