1.) Madara broke the seal. The whole 5 minute prep time he said he needed to Zetsu while waiting for the Rinnegan was to break the seal holding in Kurama.
2.) Doesn't matter who breaks the seal, once broken and extracted, the host has only the amount of time their chakra allows them to have.
Naruto is definitely not dead, the manga is about him, so that's kind of obvious. Not sure who told you he was dead. Kurama most likely did something to further prolong Naruto's life or maybe even save it, we don't know. We'll just have to find out soon, however, the story is so far following my call on Naruto being a tragic hero. His destiny was foreseen prior to his birth as being the one to save the world. However, they didn't say at what cost it would be to save. So far, the death of many and most likely, even the death of Naruto is required to save the world. He wants to give the world a reason to stop fighting, and what better way than to show the world that he will stand and fight for not just his friends, but for other countries as well, and even sacrifice himself to save them all.