Well... I've been busy with everything but this, unfortunately. I've made a little progress.
First was to use some of the timber shavings I'd saved to fill the top side of the neck pickup route. It was just a little too tight on the edge of the pickguard. I overfilled it, then cleaned it up with a chisel.

In advance of paint, given we're talking Ash, it seemed prudent to do some grain filling. So I went and purchased some TimberMate, and given colour wasn't a stress (I'm still being told it'll be painted by the boy), I went ebony. That also helped me check for any grooves where I'd enlarged comfort carves (think I did ok). It's now sanded to 400 grit.

Rear view:
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I think that shows the enlarged or extra carves (belly cut and neck plate) fairly well, thanks to the TimberMate.

Front view:
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Overall, I'm reasonably happy. I ran the TimberMate too wet during its first application (I did two coats) - it wasn't a slurry, it wasn't 15% water, I spilled in too much. So painting it on was like painting water. Most of the body has come up very well. But I think I need to redo three smaller locations, including the forearm carve.
I've got two fine cracks that are open (need filling - one area, one of the cracks is the body seam), a roughish spot on a radius/edge, and the forearm carve I've taken a little too much off - the TimberMate came off a little more than the timber, and I can feel the wave of the grain again.

Given the TimberMate went on very wet, it also went into the neck pocket. Which is now too tight again. So I'll need to sand that back, too... It's a very, very fine coat - I scraped it out - but you can see the TimberMate in all the cavities. I've sanded back everywhere I can in the cavities - I'm hoping that it's sufficient for the primer/basecoat, and the copper shielding tape.
You can also see the extent of the filling in the neck pickup route, which has retained more of the TimberMate than the area around it.

If you've any tips, I'm more than open to them.