(b) Idea – primaryFrom what I've read, I really feel like the idea of "man vs. nature" is holding the entire story together. There's this huge toxic forest with all these nasty bugs pushing humanity back into these little corners of the earth as they fight for resources and push back against the forest. This over-arching idea of conflict between man and nature is the main point of interest in the story that drives all the characters to act the way they do.
PG-13. There's fighting, but no gore is depicted. It's mostly explosions and people being knocked out. Occasionally there's a little blood and the violence gets a little more intense (people die, and are killed by other people) but I think it's done in a very tasteful way.
Miyazaki indirectly borrows both from Greek mythology (in "The Odyssey" there's a princess by the same name as the main character/book title "Nausicaa") and according to Wikipedia, an ancient Japanese story "The Princess who loved insects" which is about a girl who loves nature more than getting caught up with things that can seem more superficial in life (like courting, and putting on make-up, etc.) I think Miyazaki must have had some understanding of Environmental Science to create the layers of evolution from dead insects to overgrowing fungi forests (way cool!) found in this book.
-Also, while reading up on a version of "The Princess who loved insects," it mentions that one of the things this Princess refuses to do is die her teeth black. Sounds gross, but apparently it (Ohaguro) was a real custom done back in the day. The significance of blackened teeth changed slightly over time and is still practiced today in some areas... also, it prevents cavaties!!
If I decide to go with an idea that's heavily influenced by culture, it would be wise to do LOTS of research on that culture. I wouldn't necessarily incorporate historical facts of that culture, but just being aware of these things would better inform details of story, and even could possibly genereate more layers to the story. (in reference to the whole thing about black teeth.. lots of little interesting ideas could be pulled from that)
I'm seeing that the more I research I do on something someone has made, there's more research to discover from them that went into making that thing.