1), 2) There is not much difference in using more than 9 calibration points than using 9 calibration points. It will affect the result of the calibration a little bit, making it a little bit better, but not much or even noticeable. It is usually not worth the extra effort of long calibration time and tedious procedure for the user to stay focused.
3) You can not change the number of calibration points for the Tobii EyeX software
You can experiment with as many calibration points as you want using the Tobii Gaze SDK.