The ancient mariner shares his tale with a random person he meets at a wedding. This person becomes the listener as the mariner recounts his adventures at sea.
Not sure exactly. Maybe around five. But it depends on how you interpret the story and who you consider as the ones the mariner is telling his story to.
Odysseus tells his story to the Phaeacians. They are a kind - hearted people who offer him hospitality and a chance to share his long and arduous journey.