This was fine so I cut it out (previous attempts to drill the holes from an already cut piece smashed up the wood around the corners) and after many days of laborious sanding and sawing and gluing ended up with the first box
After I posted this stuff to Twitter someone said they'd like to buy one and how much would it be, so I was encouraged by this and figured I'd need a better design and process before making any for sale.
For the second prototype I ordered some wood veneer, 3mm walnut from an etsy seller.
Turns out walnut isn't that hard a wood! Oh well. I have some 5.5mm ply lying around so I made the inner box from that and stuck the walnut on top. Overall it was much easier but still a pain to saw it all by hand and sand it just right and glue it.
Thanks folks!! @Vachi - this got me thinking about putting solar panels on it... @orkn this... is a more appropriate idea than you imagine, as given the wood theme I'm sure it would be a pencil holder, and I'm making a game about sharpening pencils for the playdate!