What is the maximum guaranteed distance between the softstarter ATS48 & the motor?
The official limit guaranteed is about 100m between ATS48 & Motor.
However, There is applications working without any problem between 300m and 400m non shielded between the ATS48 & Motor.
Over the limit you may have problems of PHF tripping due to a too high cable capacitance which may perturb the synchronization. So, to reduce the perturbation from the motor cable, you need to reduce its capacitance to the earth: do not use shielded cable, use cable with low capacitance to earth.
Even in the Cascading at any given point of time you start one motor with one VFD, You have to size the cable section to limit the line voltage drop, it's the only limitation