8) How many types of people?
The people in your world are the most important factor, more important than anything else discussed so far. This is because your characters come from your people, and more often than not so does your conflict. People are the thinking factor of your story and your world. They are the ones who can drastically change landscapes, and cause simple misunderstanding to evolve into massive conflicts.
If there are only humans inhabiting your world the conflict is as character driven as it is event driven. What the humans do, to each other or to the environment, will play a role. If you have humans and elves, events and interactions between the two peoples will help drive the conflict and the plot of your story.
Many science-fiction stories revolve around human interaction with aliens of a different planet. Whether it be an alien invasion of Earth, or earthlings traveling to other planets and encountering other intelligent life forms. What happens when that first contact occurs is the driving force of the story.
Several fantasy stories involve either the return of a magical race or species returning to a human world where magic has been relegated to non-existence. Or vice-versa, where a human who doesn't believe in magic, somehow manages to enter a magical realm, or world, that throws everything they know out the window.
Then there are the stories that don't involve humans at all. Stories where your primary people are not people at all, but animals. Then you have to consider the types of interactions that might occur between different species of animals, and if there are any, between the animals and the humans in the story.
You have to remember, no matter what genre you're writing, the people in your story are the story.