So the first time I soldered the new boards the SoM was still not booting.
Quite frustrating, then in a fluke accident I found out that the "ONOFF" pin is actually a pin from the PMIC and by connecting it to 5V and then letting it float again (e.g. "button press" with a piece of wire) makes it boot.
I then solderd up a second board with all components and was able to SSH into the Linux via a USB to Ethernet adapter.
So some stuff is working!
On the HDMI side I unfortunately missed the pull up resistors on the EDID lines so that seems to not work atm.
Also the CPU debug serial does not come up. Not sure what the issue there is, might be an issue with the level shifter or I got the wrong UART all together.
Here are some photos of the process and the finished board: