The great thing about this story is that it doesn't take place in a vacuum. There have to be other people that float in and out of scenes and lives, and sometimes just get mentioned in passing. Those people add flavor and depth to the story.
Think about how dry Harry Potter would have been without the charcaters that didn't get much page time - the backbone of the story was about Harry, Ron, and Hermione - but without the other students and teachers the book would have been weird. A boarding school with 3 students, a headmaster, a game warden, and one teacher?
So, the world is filling out. Characters have names and a heritage. I have a spreadsheet to keep them all straight. They span the globe, both in heritage and location.
It's exciting seeing the world come to life before my eyes.