I didn't read the entire excerpt that you included with that post, but here is a thought that I have about it-- I recently (ok, like three years ago, that's "recent" for me) began a story, which quickly sprouted into a series of stories and/or vignettes all about the same group of characters. I found myself faced with a problem similar to yours, i.e., where to start the saga, what information to include and what to leave out, and blah blah. (And if I completely misunderstood your question, I'm sorry!)
And in considering all these questions, here's what I realized: Your first obligation in writing anything like this (stuff with a deadline excluded, that's more like a job, right?) is to yourself. You have to satisfy yourself when you are writing a fictional story. If there is material that you feel needs to be explained or elaborated on, then you have to do that explaining or elaborating where it feels appropriate. If you need to write a side narrative so you can keep it all straight, then you must write it all out.
Nothing makes me want to put a book down more than the writer stopping in the middle of the action to launch into an extensive explanation of someone's background, heritage, psychological make-up, or anything like that.
Instead of thinking forward to when, where, why, and how you might sell the finished product, realize that you don't have a finished product yet and might never get to that point if you don't first satisfy your own basic urge to tell this story the way it "wants" to be told.
I hope this was helpful!
