Aha! Now I see what you're doing. Sort of. The bulk of the story feels omniscient, told by an omniscient narrator (not the same as the original narrator), but it starts differently, in FIRST PERSON POV, not third person, either limited or omniscient.
You end up with a hybrid POV, and you risk breaking the initial promise to the reader about the story. The initial promise, as it's currently written, is that the story is in first person, narrated by a wise rat, who is the protagonist, in which case the story events will be limited to what the rat could know, and the story will be ABOUT the rat, showing how the rat's life has changed as a result of his struggles over the course of the story.
After that, the story as written became ambiguous as to POV. Technically, you could say it was still first person, and the narrator is on scene, but is observing from afar. But because the "I" disappears so completely, it may be forgotten by a reader, and the scene comes across as omniscient, through the POV of the author, not the original first-person narrator.
So, I guess the question is -- what's your intent? Is this a story being told by the rat, so that the only things that can be presented are things the rat is present for, things the rat could see/hear/feel/etc., without ever going inside the heads of the characters? Or is it a story being told by an omniscient narrator (the author), who has access to the heart and mind of the characters? If it's the latter, it would be easy to tweak the first few paragraphs a bit, commenting on how an unnamed rat (the original protagonist) views the world and, in particular, how a rat views cats. Which leads into the appearance of the protagonist.
There's a lot to like in the lead-in paragraphs, the way it lets the reader know that the protagonist is a cat, and establishing a world view, but I think you could keep much of that material in an omniscient narration (third person, not the rat's first person pov), and thereby maintain a consistent omnisciency. Or, alternatively, keep the whole thing in first person, with appearances by the narrator and reminders from time to time about where the rat is in the scene, how it knows what's going on, and so on, but without getting inside the heads of the other characters. Except then, really, readers will expect the rat to be the protagonist of the story or at least to have something at stake over the course of the story.
One thing to watch for, whichever way you go, is infodumps where you give too much backstory in big chunks. Keep the action moving and weave in little bits of backstory as you go along. But, again, there's a lot of good stuff there. I'd even go so far as to say that this does seem like the type of story where omniscient would work well, despite its challenges.
JD