So the first real progress has been made on THE PHOTOCOPIER today (title all-caps status: pending).
Making a fully 3D game inside of a few weeks is going to mean cutting corners. Since I'm aiming for horror anyway, I can have my cake and eat it by adopting a low-fi style a la Return of the Obra Dinn. I've done a bit of research and it seems like what I want is possible but it'd be really ugly... which is perfect! It's horror game after all.
So today I put together a test scene in Blender and set about decimating it with dithering and blowing out the colours. I think the result looks radical and it's been a big boost to my confidence. I particularly like how there's weird purple banding in the sky.
Now I just have to get it into the game engine...