I think the reason why Sasuke is fighting 8 tails is because we are supposed to see how the Sharringan is able to control all the mythical beasts. We had a taste of that when Sasuke entered Naruto's subconscience when they finally remet, and held back the Fox's powers.
Once we see the eyes in action, we will be able to make predictions of what power Itachi gave to Naruto in order to fight Sasuke. I also predict that this power will be in no way associated with what Naruto will learn in his Sage training.
We'll see in what way Sasuke will defeat the Jinchuriki (the weakness will be exploiting his reliance on the 8-tail's powers) And whatever that weakness is, Itachi's gift to Naruto will counter-act it.
I think that Naruto needs to learn how to maximize the Shadow Clone's abilities.
The sage training will have different tasks to complete. Pervy sage took a long time to complete them because he was one person. Naruto can do it really quickly because he can be however many he wants to. The bad part is that 1 normal shurrikan can dispel the shadow clone... Whats the point of making it then!??!
Naruto needs to become triplets, or even 6 identical shadow clones, where each one is able to hold its own, and fight as if they were the real Naruto. Pein wants to fight Naruto? Well lure Pein to a fight with a Shadow Clone Naruto far away from Konoha, and in the end the clone will vanish, and Pein will have to make his way back to Konoha again...