have you used plastcote prima? if not it will flake eventually making your hard work a waste of time

the rest of what you put sounds like you've got it in order

halfords paint is ok but expensive and the colour match could be slightly out to the original, you will proberly get butt raped by the stealers for a can of paint, have you got a paint shop or an idependant auto paint suppliers near you?
make sure you do thin cotes when you spray at each stage to avoid runs etc.