It develops I was overly conservative in my original cutting layouts, so I was able to get 6 of the main segments out of a 40x60 sheet of foamcore, and the 9 outer trim segments took only about half of the 3/16" thick black sheet.
Which means I'll have 40x30 of 1/2" white and 3/16" black left for trim pieces as I go along. This is probably a good thing, since I'm making part of this up as I go along.
I'm leaving cutting until tomorrow night since I'm sleep-deprived right now and really don't want to screw this up.
I'll add photos when I get a chance.
Just went back to my drawings. Looks like I managed an in-between small size :-(
Good thing I didn't cut tonight, and good thing I'm painting the whole thing anyway.