I would not run the motor at 5 on/5 off. That will cause the motor to vibrate at 6 hz. Keep the on/off as fast as possible.

I know of a commercial product that switches at 1/2 cycles. At 50% power it only passes the positive half of the cycles. This causes strange readings on power meters. I don't know why it does not heat the motor. Maybe it does.

It is OK to do this.
on,off,on,off,on,on,off,on,off,on,on,off,on,off,on,