Gav,
You answered so many questions, that haven't even come into my head yet.   (Blue, Grey, Yellow mask)
With my first 'traced' homemade Gottlieb stencils, even with endless hours double/triple checking, the final colour was off by a millimeter in places.  
It's taken 3-4 weekends work. Base, first, second colour down and then D'oh. Completely start again.  
This machines artwork does not have any original over spray, so the tack level of the stencil was a worry, but you have put my mind at rest.

My 20+ year old 'SATA' spray gun won't let me down. I still don't understand why someone would spend hours++++ stripping down and prepping a cabinet and then apply a stencil with an aerosol can.  

Following Nino's '8 Ball' tread, I'm thinking an automotive acrylic paint, but I can't make my mind up.  
Cheers,

Paul.

I've seen and experienced issues with the stencils from overseas.  Thankfully it looks like they have changed their mask as the previous material was that 'sticky' would lift up base and was a nightmare to put on.  There are also issues with registration from one colour to the other, so be mindful you may need to modify yours to work.
Best of luck, I don't think you can go wrong with acrylic or 2k.