dtokez:
There are PTS (push to set) terminals though which I might have a play with further down the line
That won't take long, generally only one function for those (or 2 on some panels). Push to terminate the exit timer with a possibility of being able to use the button as a doorbell in the unset state. If you have the front door contact set as exit terminate then you don't need the PTS button so it just becomes a doorbell. Might as well just fit a doorbell!
As for the GSM\SMS alarm shield, interesting idea, bearing in mind you're looking well over £100 for a manufactured alternative it's probably worth doing.