I have a lot to add to this, but not enough time, so I'll just talk about the Khahit thing:
In my mind, this concept is actually pretty simple, but it's tough to put into words. Basically it works likes this: The Bakkerverse is timeless, everything that was going to happen, was always going to happen, already happened, etc.
In addition, as dragharrow stated, the God (Absolute, Monad) is the prime mover. So here's what's going on: The God actually does speak to Kellhus, but Kelllhus is also insane. It's his insanity that's making him believe these things. But the God was/is the prime mover, the God make itself apparent in mundane things, because they were always going to happen. That's why I think Moe's line about a "lie made truth" is important. Kellhus is sort of falling into "saviorhood" without realizing it...until he realizes it. And goes insane. Which is one and the same with the god speaking to him. He was faking it up until the Umiaki.
So, like I've mentioned before, I don't think the God is (at this point in the story) some conscious agency that's "doing things". The events of history (a young Dunyain monk being sent to kill his father, a Mandate sorcerer being banished from the Empire, an Ark of aliens falling from the sky) are all movements of the God, Khahit, Fate, etc.
I do, of course, still think all of the ensouled beings have free will, it's just that the decisions they make, were the decisions
they were always going to make.
The big picture is, everything's moving towards the God awakening, via Kellhus. It's all "part of the plan", because all of these things were always going to happen. It's also why there can only be one self-moving soul -- the God itself, the All-Soul.
I strongly disagree that Kellhus will close the way to outside and make the world more deterministic and soulless. Why would he do that and how would that make him a savior? Despite their damnation and their cruelty and their arbitrariness, the hundred provide the intuitive meaning that makes life worth living. Without them it'd be the semantic apocalypse.
Without them we would no better than the Inchoroi!
That's where they came from. They're humans without the fundamentalist meaning of the hundreds. Without the hundred hedonism and power are all their is. Without the hundred our hungers would define us and we would become a race of lovers and flesh.
Hmmm...this is a tough one and I'll probably have to return to it. To me, the "meaning" attributed by the Hundred is...well, kind of meaningless. It's no better or worse than the Inchoroi. Instead, Kellhus shutting the Outside and merging all of the souls into the Solitary God may be the best possible fate anyone could hope for. He is essentially freeing all souls from material bondage (a bondage that is enforced, if not initially perpetrated, by the demiurgic Hundred), and in a way bringing true enlightenment to all ensouled beings -- all possible thinking creatures. It's an apocalypse of a different kind. It's not necessarily "good" or "bad".