Usually I'm one of those people who starts wiring and at the same time thinks about what to connect to what. That can work, but in the past it has often only partly worked. That's why I decided to do everything differently this time.
Before I started wiring, I made a plan. For this I used the tool "wireViz" (link below), which was presented a few weeks / months ago on Hackaday.com.
In the beginning it was a bit tricky and it took me a while to understand the system. But over time it all made sense and new wiring was quickly planned.
So I also planned the pneumatic connections and the USB connections (between the two cameras, control board and USB hub). The current status (see below) is not quite ready yet. In some cases, the color codes are not yet congruent with reality and some additional information is also missing. But hopefully the basic scheme can already be seen. :)
At this point, many thanks again to Daniel Rojas (https://hackaday.io/project/173240-wireviz) for this really helpful tool. (For which, by the way, I haven't found a free and comparably simple alternative.)