Hi Russell
I'm a dyed in the wool enamel user too, and I've been spraying them for years, which probably qualifies me to pass some comment
First all the advice above is good advice. You definitely don't want to start experimenting on your model, so practice on something else.
As far as thinning goes, I think it was Patrick who made the point that enamels are more tolerant of approximate thinning, and that reflects my experience too. Every set up is different and it is impossible to give an exact thinning ratio as it is dependent on many, many factors, it even varies from paint to paint, never mind manufacturer to manufacturer. However, with your enamels, I would suggest starting at a ration of about 60:40 paint to thinners. I have used cheap white spirits to thin all types of enamel paints with no problems, so I would not suggest wasting money on expensive branded versions. This may seem a higher paint to thinners ratio than many recommend, but it is a good starting point. It is easy to add a little more thinners if needed. I never measure ratios exactly but go by eye and the look of the thinned paint, this obviously requires experience and can't really be taught, but then that's what practice is for!
Perhaps the other most relevant factor, along with the thinning of the medium, is the pressure at which you spray. I spray at a much higher pressure than most hobby sprayers and it works for me and my airbrushes. I would suggest a minimum pressure of 30 psi and don't be scared to go higher. I also spray everything from fine lines to Luftwaffe mottle at this pressure and do not understand why some people seem to fiddle about with theirs all the time. There is a tendency in the model/hobby world to overthink the issues which creates a whole new set of problems!
Airbrush spraying is actually not difficult at all, it just requires learning and practice, like any other skill.
Good luck with your project(s) and don't hesitate to ask questions, no matter how silly they may seem I can assure you that they are not
Cheers
Steve