Some of the capitalization is wonky, like capitalizing "Organization." Some of the grammar is off; you have some sentence fragments that could be eliminated.
But the greater problem is thematic. This is a pretty bare-bones tale of how the Library got started, and it's one that I don't think a lot of people are going to like very much. There's not much there, and what is there clashes very badly with the image a lot of the people have of the Wanderer's Library as its own, very old, very powerful thing.
Different takes can be interesting, and succeed on those grounds, but here, the Wanderer's Library is taking the place of a generic doom that the Foundation accidentally made. I don't think it's very compelling.
As far as "is this realistic," well, you're asking us to make that determination about dread eldritch rituals. But I would say the following:
1. How did this guy find the knowledge about the Library's true intentions if the Library is deliberately omitting knowledge for its own purposes? Why would it give away the game? You completely skip over the all important question of "How does he know any of this?"
And, while the next two items are just my personal interpretations, you did sort of ask, so:
1. While I tend to view the Foundation on the low end of the power curve compared to others, I would not attribute to the Foundation sufficient power to create the Wanderer's Library.
2. I wouldn't attribute sufficient power to the Wanderer's Library to eat a reality.
What I would suggest, personally, is as follows:
1. Don't just tell us how the Library actually started (though see #3). Show us the process of this man's research. Show us him fleeing the Foundation, show him joining the Hand, show him becoming entranced by the Library, show him starting to research it. That's going to be a lot of build-up, but it will help things flow more organically.
2. Drop the intro. Have him make entries chronologically, like it's actually a journal. The reader doesn't find out things are very, very wrong until later in the series (I'm assuming, from the Part 0, that this is intended to be a series). Indeed, until then, things may seem to be going very, very well. The Hand could use this guy's knowledge to do a lot of good.
3. Consider lowering the stakes. The Wanderer's Library doesn't need to be eating entire realities, it can simply be absorbing parts of other libraries into itself (taking them away from the veiled world in the process and ruining lives), sucking knowledge out of people's heads, stealing archaeological and biological artifacts for its archives, and so on. There's enough material there for conflict without causing the apocalypse. The Foundation doesn't need to have created the Library, it can have just screwed up its functioning, it might not be involved at all and another force has caused these problems.
