If your spindle case isn't earthed strange things can happen. It's easy to unscrew the endcap and solder an earth wire in on pin 4, or you could just connect the earth wire to the spindle mount assuming it's metal.

The minimum frequency setting you found, PD11=100Hz, is meant for air cooled motors which burn out when run at too low a speed, due to insufficient airflow. For the water cooled spindles this can be set much lower, however don't expect to get much torque below about 50hz.

PD144=3000 is just a scale factor which makes the rpm display show the correct numbers. You can also set PD14 and PD15 to increase the acceleration/deceleration. They're the ramp-up/down times in seconds, so just decrease them until it's fast enough without faulting.