If I'm talking about a short story, is 物語 the right word to use? Does it make a difference if I'm talking about a short 30 page manga story verses a story that is 30 pages of text? I googled monogatari, but I couldn't find a page that explains if I need to make a distinction.
30 pages is long enough to be called a 物語, but note that its meaning is somewhere between "tale", "legend" and generic "story". If your story is something like Harry Potter or Titanic, it's safely a 物語. If it's a news story or someone's matter-of-fact success story, 物語 is probably not a suitable word.