I don't think you're going to get much help here in the Advice and Techniques subforum. Well, I'll answer anyways.
1. To be quite honest, I don't find any of those particularly effective. Of them the most effective, or least ineffective, would probably be tempo, because it's somewhat difficult to convey, for example, passionate fury in larghissimo. But you can do so many different things using the same element of composition. I usually include written instructions for what emotion should be conveyed because the score itself is so insufficient.
2. As said, tempo is probably the most effective at conveying different degrees of passion. But again, I'm iffy about even calling tempo very effective.
3. I don't really like how this question assumes you're composing for film. Nowhere in this post do you specify you're looking for film composers, so it's implied that it's just a given that you're composing for a film rather than for the love of writing music. I myself didn't take it that personally, but I don't think it's too far-fetched that others here have. (In any case, I haven't ever written for a film, so I can't answer.)
4. Don't overstress about simply writing "dolce" on your score and calling it a day.
