The initial prototype PCB worked great for singles, but now I want to start selling kits, so I need to panelize them. Initially I just slapped a few of the boarrds together and added a few tabs to connect them, but when I submitted that to be fabricated, it got rejected. So today I sat down and panelized them properly:

I could probably pack them denser, and get less problems with the "mouse bites" somehow, but I think this is good enough for now. This will give me 160 PCBs in total. I varied the silkscreen on them slightly, to give them different facial expressions. Ordered them on white PCB with black silkscreen. Should arrive in a few weeks — in the mean time I need to figure out how to package the components, in particular, how to mark the colors of the LEDs.