So, one of the goals for this stage of development is to provide higher-level overviews of the data, including graphical views. After spending a few hours looking at the various C-library charting solutions, I'm beginning to favour just creating the graphics as SVG vector images using a very lightweight library called SVGdraw. That will mean a lot of low-level graph-layout code, but I've done that enough over the years that it looks like less work than trying to get the 4 or 5 dependencies built for Win32 that would be needed for the other solutions.

Will see how my opinion of that level of difficulty looks after a few hours of implementation I suppose.