Write Away

That's a good question. As already said, I'd imagine that a short story should be more narrow in scope. But you don't want it to feel like a weaker story, either. I think the world, the atmosphere and the characters should be just as developed, but you have to use fewer words to express them to the audience.

I would probably recommend having an idea of what you want to happen in your story before you write, just to have a rough plan of how long it will be. You'll probably not want to have more than two or three "real" leading characters, depending on the length.

Maybe look at your favorite short stories and see what they do that you like, how many characters they have, what kind of detail they use and how long they are?