Use a 10 kΩ potentiometer for external speed adjustment.
Turn the RV adjustment on the controller fully counterclockwise.
It depends on the controller model. Controllers equipped with RS232 or RS485 communication interfaces can support this function.
No. A BLDC motor requires a suitable controller for electronic commutation and speed control.
The available duty cycle depends on the motor model, load, speed, controller settings and cooling conditions. Please refer to the datasheet of the selected motor.