The kit is probably designed to replace your 6?-speed freewheel with a pair of single-speed freewheels.
No cassettes or plain sprockets here.
You'll need to unscrew the freewheel body from the hub first.
This kind of motors do exist, but i'm afraid they're somewhat expensive.
https://ebike.heinzmann.com/en/systems/cargopower/motor
Geared but clutchless, single-sided version is available too.
Aren't these motors rated 360 RPM no-load at 24V after reduction ? http://www.cyclone-tw.com/dc24.htm
Or 3600 RPM before reduction https://endless-sphere.com/forums/viewtopic.php?t=13423&start=31
- which means something around 150 RPM/V.
So 8500 - 9000 at 60V seems just right to me.
The motor is claimed to produce torque over 4Nm?
If so,the CSK12 seems to have pretty hard times here, transferring the
torque up to ~25Nm - this is 2.7 times of it's nominal value, which is 9.3Nm.
OK, Stieber says Tmax=2xTn, but 18.6Nm is still not enough.
Or are my calculations wrong?
You'll need just one more cable.
https://www.aliexpress.com/store/product/Waterproof-Motor-Cable-Motor-Wire-Motor-Connector/738588_32816702314.html?spm=2114.12010612.8148356.11.6385e7d1Y8zLu3
2nd or 3nd version, depending on your controller placement.