Yeah the notes showing on the melody menu would be good. It was definitely a challenge to memorize the longer melodies, especially the last one!
As for why they respond to melodies, that concept got a little lost during the short development time, but it was originally related to how Fletcher is the only natural born. The music was a metaphor for his humanity, that everyone else had lost because they had all modified themselves with technology, brain implants, etc. During the game you learn new notes by helping the other characters find a bit of their humanity again.