Of course! There is no secret formula to a good game, it's about testing the game and trying out what feels right! The things I noticed are just suggestions.
1. I totally understand you wanting it to be forgiving. It is only the instruments with the least notes. It felt like it accepted me spamming the keys. If someone starts with one of the easy instruments, and their spamming is accepted they might think about it.
If the player thinks too much about it, it might disturb the flow of the game. I'm thinking about the overanalyzing-type of players. But it is difficult to make a game that pleases everyone so don't pay too much attention to that. :)
2. Yes! Exactly! Don't wait until the section has finished playing, but just wait a half second before the Rhythm Panel closes, and show the player some positive visual feedback.
I wanted to finish the note before the the Rhythm Panel closed. It felt more like the game played the note, and not the me.
3. I agree. ^^
I'm glad you could use my suggestions, or at least thought about them! Your game already is a masterpiece. Short, cute and with an attention to detail. My favourite type of game. c: