The next thing you should complete is finish Ziost. From what I am understanding, the new expansion where start where we left off so Ziost may end up being a perquisite in order to start the expansion. The other thing to note is if you start the expansion without doing this, you won’t be able to go back and do this so make sure you do this if you really want to see the storyline. Also finish everything on the planet before you finish it as won’t be able to go back once you finish the storyline for the planet.