So without a motherboard the case fans from corsair are pretty useless on their own. But they can just be used as ARGB fans, if you change the pins from the fan. And since we don't have a normal motherboard anyway, and I don't want to waste cycles on ARGB on the printer MCU, I made a small controller out of a spare ESP32 using the RMT driver. 

I also had to combine the 3 fans into one connector to the printer board, so I had to leave out 2 of the tacho signals. I routed one of the signals to the ESP32 so it can be used to read out the speed using the PCNT driver.  I use this speed to change the colors / animations of the fans.

The Jonsbo case has a weird little PCIE cover to facilitate the front screen HDMI / USB connections. These just happen to fit the antenna from the CM4 wireless just fine! To mount everything in place I cut a piece of aluminium into the size of a motherboard, drilled some holes and fixed the printer board (and other peripherals that are planned) to the aluminium board. I can then simply remove the "motherboard" as if it is an ATX one.