I'm glad you like that pouch, but be aware that it is pure conjectural folk art... I made it to go with a .40 cal Tennessee rifle and an original horn, and in the spirit of original pouches seen in the books by Madison Grant and Jim Webb.
To answer your question about research and ideas I look at those books and also try to get a peek at original pouches and horns whenever I can, either on the contemporary maker's blog, long rifle shows, pictures and guidance from more knowledgeable friends and acquaintances, and the rare in-person and non-rushed examination of one when it presents itself. And of course many contemporary makers are a big influence on me personally.
There is no one source of actual documented hunting pouches from a specific time and place that I'm aware of, you sort of have to look all over and dig. Powder horns seem to enjoy a greater level of documentation and accessibility.