I've made some progress!
Firstly I plugged that hole in the bottom! Mine didn't come with the screw-in extension, and the strap button used is just another bridge pin. I want to use normal strap buttons, not something that can unscrew itself easily, so I whittled down some hardwood dowel and bashed it in.
I used Gorilla glue, because I never said I was a luthier!
then onto the grain filling. I watched some Youtube videos from people building Les Pauls. As I'm not spraying anything I don't really have a chance to either seal the wood prior to filling or use a tinted lacquer on top. My compromise is to grain fill then sand that back level with the wood. Then apply stain and lacquer over this.
That is my office chair in the background. This is week 46 of working from home. It doesn't look like this is going to change any time soon either.
I went outside to sand the grain filler back back:
Then a wee bit of staining:
Our cats knock those plant pots over every time we go outside, so I've given up righting them.
Looks like a piece of wood now! I've used a mix of teak, mahogany and oak woodstains. I want the bass to be red-brown rather than a lurid cherry red, and light enough that you can see the filled grain. I don't want it to look like light wood with an unusually dark grain marching over it, so this is a nice middle-ground.