Re #1: Characters can provide multiple narrative functions, although it’s also possible to zero in on their primary role, then see how they don other archetype ‘masks’ to achieve their ends. Any character can wear any archetype mask in any scene and any relationship.
Re #2: Titles can be huge. Like ‘Honey, I Shrunk the Kids.’ Or as you noted ‘Snakes on a Plane.’
Re #3: Your point is valid. If a script reader feels like a choice a character makes is not something they would do, but more like what the writer needs to have done to service the plot, then you run the risk of losing them. The way to avoid this issue: Immerse yourself in the lives of your characters and make sure choices derive or at least align with them.