Found a way to mount everything in the bamboo case. I'm using knurled insert nuts with shallowly drilled holes. It works great, as you can see in the above picture.

Here's all the empty nuts. The bottom right was going to be for a small usb hub, but space was too tight, so I decided against it. Instead, this will be where the extra solar panel power cable can be coiled. Unfortunately I drilled a couple of the holes too deep, so now the case has, uh, speed holes. The velcro in the top right is for the battery.

I also attached the hinges and clasps, and then cut the part of the screws that stuck into the case with a dremel.

Finally, I redid all the wiring from the keyboard to the rasbperry pi pico controller. It looks a lot cleaner now, but unfortunately, I seem to have burnt out my pico de-soldering all the bits of stranded wire.

Also ditched the velcro cable ties for the less bulky and thematically appropriate garden ties. I drilled some holes in the bottom and threaded more cable ties through in order to secure the keyboard plate to the case. It all worked out pretty well.