The series is bad. REALLY bad.
That being said, I did determine that the opening should focus on the discovery of the "fallen to earth" figure (Gandalf, probably).
The Lord of the Rings, as well as The Hobbit, both start small. And then it slowly introduces you to the world of Middle Earth. You grow to like the main characters, then you travel with them as they explore the world around them. This should be the approach of a fanedit of Rings of Power.
Rings of Power is like a Dump Truck backing into your living room, dumping a bunch of fantasy tropes into your house, and driving off with the driver shouting out, "There, make sense of that, Jimmy!"
So, my suggestion is to start with the Harfoot discovery of Gandalf (or Gandalf-like character) and slowly develop the story from there... avoid dealing with the other story lines EXCEPT when they will start to overlap with this main focus.