Long story short - each character/instrument combination was a different file, at 24fps, synchronized using kdenlive. I put them all together in one (first by linking it, then by copy/pasting, so that I could properly make minute edits). There's some of everything here. A lot of warp layers, a few imported svgs, a few pngs, a LOT of animated parameters, and MANY MANY time loops. Also lots of keyframes on exported canvases. Also the multiplane effect. Lots of tracing of source pngs. Some things which aren't obvious - the player of the purple violin (Rose) has hair that his blowing in the wind.
WEIRD ISSUE: Neither Synfig (via command line) or Synfig Studio would render frame 1563 (1m 5s 3f). I had to render 0-1562 and then 1564-3959. Also I rendered this at 1280x720, which took 20 hours or so (I couldn't get the multithread encoding to work properly, the command line should be better explained - which are the default options, which are the specific options?).