Two long evenings later, a layout was born and a first prototype ordered.

Well first prototype is nice to say, considering the short time available it will propably be the final version.

The rest of the circuit is pretty straightforward. WIth the shift register i managed to have only 2 free pins left (besides the programming pins). Also the driver/register has this nice function that it limits the current for us. No need for resistors, some cents saved.
Oscillator? No need, internal is good enough.
Voltage regulator/supervisor? No need, input range of the components is wide enough.
It would be possible to multiplex the inputs too but there is no need here.
In hindsight the only critical thing i forgot for now would be a diode for reverse polarity protection.
But that would bring down the already low 3V from the planned AA batteries. Which reminds me that the driver wants a VCC of 3V-5V.
Quite Exciting. The datasheet does not mention any undervoltage lockout. Will it work? Only the first assembly will show.