3D printed parts are ready and I screwed in M3 16mm screws, that are a size too small and about 19mm too short - so I ordered some M4 35mm screws with nuts on eBay and probably payed too much. The fans seem to be not the most powerful fans, what makes sense since they cost about 3 Euros each. I might use some incense sticks and a black background to make a photo project out of it. The humming of 4 fans is noticeable, but hopefully some PWM will bring it down.