Metal case connected to ground? Well, I think I don’t understand why you’re giving a note on this.
Just to ensure that we have the same understanding 
However, the case is connected to my signal ground with the two M3 screws. Probably the case ground lug of the fader also needs to be the reference ground for the touch sensor?
Not for the touch sensor, but as a good shield against noise (which would result into jitter).
A perfect ground connection to the case is important, the connections via M3 screws are not sufficient.
Honestly I think I will just buy three bcf2000 rather than doing a midibox because buying the motorfaders seperately is about the same price than buying the hole bcf2000. (haven’t asked albs/Balthasar Schmidt but they’re 22€@ebay)
If you want to save money, it’s a good choice.
The motorfader project was created before BCF2000 came to the market, today I probably wouldn’t do the effort anymore.
Do you accidently know what the supply voltage at the linear track of the bcf2000 is? Because i would like to connect the bcf ground to the analog ground of my mixer and try to control the vca’s controlvoltage with this voltage. (vca fader in an old analog desk)
We opened a BCF2000 case long time ago in doc’s lab - the construction is impressively compact, faders and motors are directly soldered on a PCB. It was too hard (and dangerous) to find a way to control the faders directly with the core module.
We haven’t measured voltages, but it can be assumed that they are either 0-5V or 0-3.3V
Isn’t it possible to use an MF module with ain + the AoutNG?
Yes, thats possible softwarewise, but the idea to connect the VCA CV directly to the MF wiper wasn’t so bad, I think that this will already work, so that no AOUT module is required.
(if you need a frontpanel, let me know - would make prototype panels for free to support the midibox projects if that helps… fpd files will work fine)
I would need a frontpanel for my 16x16 BLM - I will write you a separate PM 
Best Regards, Thorsten.