Thanks for the tips, Simon.
I was leaving it as long as I was, and sanding between coats because I'd read that in the guide. After reading your post a couple of times, I may have sped up my timeline a bit. I did get finer and finer with my sandpaper - with the view to just "touch" the surface and scuff it a little bit to take the next coat. In the end, I ended up putting on 6 coats of colour, and about the same of clear on the body. I went with about 4 coats of clear on the neck.
Before putting the clear on the neck, I did do a touch more work with the Shinto rasp on the headstock, and tidied that up a bit more, and made it a little more respectable - hopefully you can see that in the photos below.
I hadn't worked with a soldering iron for a while, so that part was a bit daunting to begin with, but I made it work.

Ultimately, I feel like it came up a treat. A few friends who i showed photos of it to were impressed, too.
Lastly (and I feel, most importantly), the "customer" for this one seems to like it, too.

After finishing this one and reflecting on some lessons from it, I feel confident to take on an IB-5, but this time, I'll probably spray paint it with the air compressor I got for Christmas, as well as make a few changes to my process in general.