I've got this story idea. In the story, this guy, named Doc, goes to several alternate realities to find people he deems useful to him. He needs to gather people to stop his brother who is doing the same thing. His brother is attempting to force all realities together and, in the resulting confusion, make himself leader of this new, singular reality. But I've found a problem. In order for Doc to decide that people he gathers are good enough, he went through their lives and adventures. What I'm trying to say here is that every MC in this story will have, themselves, already gone through their own "big adventure" (I mean the kind that would go into a book). Now, this doesn't mean that the characters won't grow throughout the story, just that they are already mature adults (At least, most of them are mature). You see, if I write each of their stories individually, before I write the story that is the subject of this post (I'll call it "Subject Story" from now on), I'm worried that some people won't have seen every character when they pick up the Subject Story, and feel like the other characters just appeared out of nowhere. However, if I write the Subject Story first, then the reader will know each of these characters, and be able to the read about the adventure that made them who they are in the Subject Story. But, if I write the Subject Story first, with all of these characters who already have a past that they would reference a lot- Oh, right, I should mention that each MC's reality runs on it's own set of rules (Magic, history, geography, etc.), which would definitely be referenced by them- I'm worried that the readers will feel overwhelmed by the five, maybe six different worlds that come with each character all in one story. Another point: If I write the individual characters' stories first, then the reader will go into this story knowing all of the characters and wouldn't be troubled by each different world that comes with them. Finally, I could just not write the individual stories, but then I would have these five, maybe six worlds that are barely explored and it would leave a sour taste in my mouth to just let them go after creating MCs for each of them. I guess, I'm asking what the general public thinks. Which adventure should I write first? The collaborative Second Adventure, or the discrete First Adventure?