Don't have all parts yet, but enough to get started. I've send two PCBs to @Alex as well - but I have a head start ;)
We had to figure out some errata ourselves, since we've ordered boards that weren't the final version apparently. The BOM itself is also different now. The MOSFET in our version had to be soldered on in dead-bug style and turned by some degrees.
The badge worked in the end and I did two small modifications: the simple add-on was powered from the batteries, I changed that to also get 3.3V from the regulator. There was also a good use-case for an additional reset button, so I did that.
The badge worked great after the latest firmware was pushed on it, very happy with the result!
The 3d printed buttons arrived from JLCPCB, a long with the expander PCB, so this is complete now :)