After far too many weeks of research, noodling, and outlining, none of which seemed to be going anywhere, I decided to adopt a new strategy: just start writing. I'm driving cross-country in the dark with no map, no destination, and no visibility beyond the reach of my headlights. It feels weird and I can see plenty of problems in what I've written so far, which I know will have to be heavily edited when I'm done, but at least I'm putting down words and it feels good.
This is an unusual writing strategy for me, but for the moment it seems to be working. This book is not like anything else I've written because I'm already familiar with (a version of) the characters and setting and because it's structured as a collection of related short stories. I was beating myself up about the linking überplot and character arc that ties them all together, but I've given up on that for now. I'm just writing one story about these characters (not even necessarily the first story in the book), and when I'm done with that one I'll write another, and after I've written a few I bet I'll understand what bigger things are happening and I'll be able to put the stories I have into the correct order and insert the necessary bits to expose to the reader the überplot that, in some subconscious way, was there all along.
I'm putting a lot of trust in my subconscious here. This is kind of the opposite progression from what jaylake did with his New Model Process a year or two ago, but then his process and mine started off very different and I'm sure we have different lessons to learn.
Alas, the writing isn't going any faster this way -- still about 500 words a day -- but at least I'm moving.