If you are claiming a discount on your insurance policy for having an alarm, then they could use this fact to refuse to pay out. There may also be a requirement to have it serviced regularly by a suitably qualified and licenced person. You policy terms and conditions should state this.
no, because of the layout of the house and drive it's a pain to use the front door if going out in the car.
I have looked into getting a second keypad put at the back door but I think the alarm system is old enough that it would mean a keypad and new alarm box unit which is nearly the same as fitting a new alarm.