After quite some while, I can present some progress.
All 182 handles are working fine. I controll them over 13 ESP32 MCU. Between the "master" and the "slaves" (I know, this does not exist with ESP-NOW) I communicate with ESP-NOW. In future, an ANDROID app will controll the master.
The communication between the slave ESP32 and the stepper drivers, is via I2C and - don't follow this!! - Dupont wires.
I learned the hard way, what seems to be obvious to all experienced makers...
Dupont = prototyping
Dupont = NOT for large scale and/or permanent installations!
They are simply not reliable. So I need to change to JST-XH... All of them... outch :-(
The PCBs with the motors are hold by a bracket which is screwed to a support on the wooden frame. With this, I can exchange easily individual PCBs later. Also they are interchangeable. I think, this almost 100h of 3D printing was worth the effort.