Finished the painting a couple of days ago, spent yesterday merging and splitting layers and repainting small sections that only get seen for a few seconds as the camera moves. I've currently got around 30-35 layers that made it through to aftereffects. As a bonus, a screengrab of my workspace in Aftereffects, with a nifty 3 quarter-ish view of everything- almost in place.
Today I'm focusing on the camera's path and getting some of the smaller particle systems in place.