No length limits upper or lower, pages or words or otherwise. It just has to be a self-contained, one-chapter story. One year Cutlerine (who is crazy man, how I miss him) submitted an entry that was almost 18,000 words long (like I said, crazy man). On the other hand one year I submitted one that was only 1,600 words and it did okay too. It all depends on how much you have to say.
As for submitting your entry, what I and other FF&W (ir)regulars do is write our story in a word processor, then copy that into the message body. That's how we post stories/chapters in the main FF&W forum. If you're worried about weird things happening with formatting upon copypasting and would prefer to attach it, that'd be up to the judges, but as a rule we prefer to have stories published directly in posts/messages because that way we know everyone sees the same thing.
Good luck!