*newbie to which Z is refering
*
I think this part plays an essential role when it comes to card/metagame development. All things start in theory and thought.
That being said, what sort of research material are you looking for and to what end/purpose? Im assuming its for card ideas. Anyways I know of a number of indian tribes with rich histories and mythologies that could be a great asset. I wont promise anything (Elements is fun but have constraints on my time to consider) but if I happen to come across a website or something that I think could be helpful I will see if I remember to post it.
In the meantime I highly suggest looking into indian, philpino, and african mythology. All have a rich history and several unique traditions that could help bring about a spring of inspiration. Best of luck in your goal, whatever it may be.
edit: Im sorry. I had only really skimmed your list of links the first time. I see you already have native american and african. Sorry bout that >_<"