I believe during an episode during the filler arc with the three tails/crystal user...
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Without looking it up, is that the episode Naruto uses the rasen-shiriken on Kakazu? If it is, then I'm guessing you've noticed his eyes looked like the kyuubi's but blue. In my opinion, I think he was just using some of the kyuubi's chakra to use that attack, but not changing into the kyuubi form.
Chapter 299 was the first time Naruto went kyuubi.
Prior to Naruto being Kyuubi's jinchuuriki, Naruto's mom, Uzumaki Kushina, was Kyuubi's second jinchuuriki. When Naruto was born the seal grew very weak and Madara managed to break the seal and use the Sharingan to control Kyuubi's mind and force him to attack Konoha. Nobody really sent him, he was freed from his seal but then the Yondaime sealed him into Naruto.
Well I'm going out on a limb here but if Naruto dies and Sasuke destroys the leaf village I'm pretty sure, Naruto will no longer be alive and the leaf village will be destroyed
If Naruto controls the Nine-Tailed Fox' his chakra is greatly improved, thus being able to use more jutsu. Note: His taijutsu also undergoes a tremendous transformation.