Holy difficulty batman! It's been a while since I've done a Guitar Hero game, so I'm a bit rusty. I think this is an interesting idea to center an RPG around, but you may want to start with a simpler (read: fewer key presses per second) song to introduce the players to. If you haven't done it, check out what most rhythm games start out with, difficulty wise. Even when I was playing these sorts of games semi-regularly, I don't think I could've kept up with the demo song.
That being said, I really like the concept of what you're going for and hope that you'll keep working on this and tie the rhythm gameplay in with the RPG elements. I think it could be a fun combo to play through.