Hi again, Robert,
You are right that flat painting is a bit different. The techniques used are more like painting on a canvas than on a 3-D figure. The articles cited above in HM are an excellent starting place. Di Franco is a master of the flat, so anything by him is worth a look.
Also, if you can get Mick Taylor's book on flats - "The Art of the Flat Tin Figure" ISBN #1-85915-070-5 - this is the bible on this subject, IMHO. The book has been out of print for a while but if you can find a copy in English it is worth whatever you have to pay.
Flats are a "whole 'nother thing." However, don't be put off. If the bug has bitten you, I really encourage you to pursue it. Your first efforts may not be show level quality, but you have to learn a different way of seeing and representing light and shapes. I think learning flats will make a better 3-D painter of you as well. The only way you will know how good you are or how much you will like it is to try one, and this one is as good as any. They're relatively cheap so if you are unhappy you have lost only your time - which you will recoup the benefits of on other work. Also, there are dealers in the USA that carry them. You'll find them at the MFCA and LI shows in the East, and I think Chicago too. So, to paraphrase the potao chip folks: "Paint all you want, we'll make more."
After all, we are here to have some fun, right? Nobody is looking over your shoulder while you are at your workbench!! Take a look at my slide show below - there are a few flats there. The hussar and the viking ship are examples of framed flats; the indian is mounted straight up and painted on both sides and has groundwork. Then do a little research to see how others are presented. Give it a try and see what its all about. If its not for you , that's ok too!
Last tip - if you decide you don't want to paint it, polish it, and put a black wash over it and let it seep into the low areas. Then, gently buff the raised areas and display it as is.
Good luck.