Just clearing a doubt. Wouldn't adding resistor actually slow down charging of the cap and there by slowly start the motor ?
No, it wouldn't, because the capacitor and resistor are in parallel with the motor, the full voltage will be applied to the motor, as soon as the power is applied and it will start at full speed. The extra current, required to charge the capacitor, will be added to the motor's inrush current.
You could theoretically connect a large inductor in series with the motor, to soft start it, but the inductor would need to be significantly larger and heavier than the motor.
Anyway, why do you want to do this? The usual reason for soft starting a motor is because the current surge is causing the power supply's over current protection to kick in.