Here are some quick images of the current Hardware state: The Grind in the background is 5mm (~0.2'')

Two matrix-PCBs are soldered. They are also working, but I have no good images so far. 

The back with the two LED driver ICs, a STM8s microcontroller, pinheader for ESP-01 and USB-connector for power

 Can you spot the mistake on the next image?

Saw it?  The LEDs on the third not soldered Matrix PCB are soldered 180° rotated. This does not work with the main PCB. But sadly the cathode marking on the matrix PCBs is wrong. And I soldered the first five matrix PCBs wrong for the main PCB. With five not usable matrix PCBs I run out of LEDs sadly :(

Like this it should look at the end. 

Now I will work on the STM8 firmware. So far only switching all LEDs on is working.