As I'm closing in on the final version of the Gunslinger Roleplaying game I'm spending more and more time on the art and layout. I've gone back and forth from how realistic to make the art to how stylized and fantastical I want to make the illustrations. My first inclination was to be fairly realistic, but as the book took shape it became clear that a slightly more idealized art style would fit it better. So that the fantastical elements still felt in place.
Here is a page from the Character Creation chapter on the Brave character class. Along with a finalized illustration. Though I'm being idealized that doesn't mean a lot of research wasn't done on authentic wear and features. In fact I got so lost in the research it delayed the completion of the book by quite a bit. There is just too much history and details to dig into. At some point you have to edit and complete the project. I think this is why so many Western RPG's have gotten bogged down. The history and lore of the period is fascinating and becomes more so with the more you learn.
While a lot of research can be done online, trips to the local library are still important. The book has a very large bibliography and suggestions for further research. As well as a great number of films and novels. One of the best resources were the Men-at-Arms series by Osprey publishing, particularly for a lot of the harder to find images and information.