After a long pause for thought, I have moved on to the larger curved baseboard components. Three to do -
(1) the 'S'-shaped backscene for the larger scenic board
(2) the combined backscene and baseboard side for the second scenic baseboard
(3) the spline for the track bed on the second scenic baseboard.
First off is the 'S'-shaped curvy backscene. This has to be fairly robust for a variety of reasons. I am making it out of 3 layers of 2mm MDF. More
Looking again at the new fiddle yard design, I quickly realised that I didn't really need five roads on the sector plate. On the first version of the layout I built, there were relatively few static sidings around the circumference of the sector plate, so incorporating five roads was pretty essential. On the current design, there are more and longer static sidings, so there is less need for five roads on the sector plate.
Redrawing things with a 3-road sector plate immediately showed