I can TOTALLY understand what you're saying because I was in the same boat. I also struggled a lot with the same notechart mapping problem. You can use the Rap Remix engine if you want to, but you would need to modify it more than the usual in order to have different stages in the game instead of just one. And about the time, no need to worry, rushing games is exactly what makes games like Sonic 2006 be Sonic 2006. If sometimes needs to take you time, then so be it. Even if it takes you months, make sure to take your time, and obviously make sure to enjoy what you do, because if you don't, then you will leave it unfinished and hate what you created (I'm on that boat right now LOL)