Where do the Ogier come from?

Something I picked up while browsing the Wiki is the origin of Ogier. In case you were unaware, Ogier are not native to Randlands. They actually come from a parallel world (not a mirror world!). There's apparently a bit during the Great Stump scene where they talk about the Book of Translation, and whether they should leave the land so that the 4th Age may begin.

> According to Maria Simons, the notes say: "The 'finn worlds are Parallel Worlds, the Ogier world is a Parallel World. The place that Lanfear, Rand, Loial and Hurin went to was a Mirror World, as were all of the ones in the Portal Stone incident."

EDIT:

So my questions/discussion points are:

- Where do you think Ogier came from?

- Why does their leaving of the Randlands herald the 4th Age?

- How does their homeworld compare to Randlands?

- Why did they leave their homeworld?

- How did they leave? Apparently they used a book, but is the book a sa'angreal or something else? If the former, does it mean the One Power exists in parallel world as well, and are they also caught in the never ending battle against the Dark One, etc.

- Are the Steddings actual pieces of their original world, and thus why they can't leave them without feeling the Longing?

- Where do they go when they say they will leave: to a parallel world, a mirror world, or to their home world?

Feel free to discuss! :)