Thanks guys. Looks like I will have a few more parts to order then.
I like the idea of limiting this in code as well as electronically. The end goal is to also have an LCD panel attached to this for monitoring RPM etc, I briefly tested this but when the spark goes off the display becomes garbled. I think this will be difficult to eliminate as there are quite a few pins needed for the parallel display. Ill focus on getting the basics working first.
I'll get hold of some caps as they sound useful to place on inputs and the power rails. And also do as suggested with the resistor. Ill post back with the results 
Is it worth putting some sort of diode on the 12v sides of the coil?
The plug I'm using has an R its part name which I'm led to believe it means it has the resistor inside it.
Regards
Andy