How long should the music be? and should it loop?
Not sure how I missed this post, sorry for the delay.
The music I have in the game right now is 2 minutes and 40 seconds long, and it already feels a bit too long, so anything below that is fine. Also, it is easier for me to make levels from the music if the beats are mostly constant, because I have to manually adjust the rhythm to the music.
I decided to make the game less random and make it actually follow the music. For instance, in faster parts of the music there will be more bombs to avoid, and in some transitions the game will rotate. I will make a video showing how this works in case you feel like making the music around this, but obviously you're free to make it as you feel and I'll work around that.
EDIT: Forgot to mention, no it doesn't have to loop.
EDIT2: Here is the video. At the 30th beat (17 seconds in) you can see the transition in the music that leads to the game rotating.
https://www.youtube.com/watch?v=Z5jr2JtJieg