I'm a newfag and it looks like i will be missing out on quite a bit of gems if I don't do required quest in time. I'm currently on ch1 act 7 and im guessing there is a lot of story to go through before I unlock this event?

I'm also seeing "main quest fast track event" which im guessing is going to unlock Rinascita. How exactly does this work? Do i get to do whole questline in that zone, or am i getting only a few quests and then im sent back? what will happen to previous chapters?