So, it might not look like a whole lot yet, and it's not, not going to lie on that. There's a lot more work to get done on the editor side to be able to completely do all the handling I want around spritesheets and animations, and loading them all into the app - but I've gotten a good ways into new code this weekend that I had no idea about beforehand, so I'm counting that as a win.
What I've got currently processes, then animates nicely what's in the complete spritesheet. Next steps will be to be able to isolate individual frames from that, tie them back to specific facings and actions and finally output a new spritesheet with the animations used, and an associated metadata dump that I can use in the app to tie it all together into number of frames per action, the time it should take to render that entire action and all that other really really important stuff that the app cares about, that almost no gamer will ever know exists or care about (and nor should they!).
I'm currently doing a mental game of "should I?.... should I not?..." with a further optimisation of each frame of animation, or animation action - so that unused areas of the frame are cropped, and then that frame is rendered to a specific place in the overall screen, so that it all looks correct - but it uses less memory to store the bitmaps. I'm not on either side of the fence yet entirely, but certainly taking a good look at perhaps each action/facing might get an individual frame size.