My assumptions on the person stronger than Sylar is that it's an empath (same powers as Peter) and that he was involved with the Linderman group in the past. If that's true, he probably sees Molly via Charles' power (which is likely where the preminatory dreams Peter had in the beginning came from, though he seems to do much more). Charles' speech about there always being a good one seems to indicate something of the like, and there are very few ways of making someone scarier than Sylar wihtout making them just plain ridiculous.
I suspect Nathan is in fact dead, though he certainly doesn't have to be. I think it's for the best overall if he is, though. really, he isn't an especially compelling or endearing character and the best they could do to make people like him is really kill him.
Hiro's time traveling is, frankly, never coincidence. He may not have meant to end up there, but everytime he time travels it's for a damn good reason. There's alway something he has to see so that he can continue to grow. And yes, considering the banner that he had on his back that is indeed the Kensei whose sword he attempted to retrieve. From information I've come across, it seems the Kensei may actually be... Hiro's father. Apparently, Takei was playing him (according to what I've been reading), and unless he was just a stand-in that'd make him at least a direct ancestor if not his father.
They've indiated that they've planned out five seasons of storylines already, I'm certain they'll keep people interested throughout 30 episodes. In fact, I'd wager they could hook people into watching weekly without a break if they could actually keep the pace up.
You do not have the right to never be offended.
