So I had to scale back my focus and ask not: "Who's going to carry the plot?" but rather, "Who will introduce the series best?"
That is how I got my answer. Kyr, Layna and Teshen.
When I knew this, the plot changed. It became more narrow, allowing me to explore the world from the perspective of my three POV characters. The depth of the world, plot, and character interactions jumped out at me.
I picked my two end points -- Major Plot, Minor Plot (s)--and how they overlap. I introduced minor characters (who were previously major characters) briefly, and let them plant the seeds for the larger plot that will emerge in the sequel.
Book 1 is to a series like Chapter 1 is to a book:
This is my new approach, though I must admit that Silver Mask borders on a Forward, rather than a straight Chapter 1. It is the slow introduction of the world, the characters, and what is at stake. But my main characters don't and won't have the keys to see the big picture issues in the first book. They are there--for the readers to guess at--and some free short stories that I am aiming to release this summer may give even greater hints. Though those stories do not feature any of the characters from the novel-in-progress.
Perhaps it is ambitious for an aspiring author to plan a series, especially in the climate we have currently in the publishing industry, but I can only make so many concessions. Clearly, for anyone who may be reading my posts or poking through my site, I think too much :P Simple is hard for me. So I aim for it, but I still can't limit myself to just one book in a world. I admire authors who can.