Finally the PCBs from china arrived, and that with a corona-bonus in the delivery costs (70$ instead of the usual 20$ on DHL)

But at least, the PCBs all look as expected:

Found some time to assemble and test the main board as well. The Buck Converter delivered 5.04V - good enough for 1 bit computer! To my surprise, the card-edge-connectors hold the single PCB Modules better than expected as well, which were the only thing that worried me.