Since the first step was working now without the top, I redesigned a the top to add a mounting for the IMU and hole to screw in a possible cover later:

Then I used some UV curing paint to protect the copper around the spring mounts for short circuits:

And finally I glued in the magnets as well as the IMU and sticked the feathers to the pins. Then soldering the Top to the PCB finished the build process.

And then turning it on, signals from all sensors arrive! Data I can work with

Findings:

• springs had been definitvely much to strong. Despite the weight I basically move always the full knob and not the top only.
• The signals of the magnetic sensors  semas somehow again strange, maybe saturation effects or sinbgularities in the field ? Something I have to investigate more closely [Update: confirmed, simulation gave me >2mT which is >20GAUSS way more than the sensors can measure .. I have to ordner much smaller magnets ...]
  • one sensor stuck at 0 (2-blue), 
  • one very low signal (3-orange), 
  • two with sudden jumps (3-green, 3-blue)
  • some signals very noisy (2-orange, 3-blue)

[Update - Quickfix]

Softer springs & single magnet on top of the top :-) ==> Touch and feel much better and no signals in saturation. Possible something to play until the smaller magnets arrive :-)

or more systematically the output of megnet sensor #1