1. (SPOILER)Auron went back to Yunalesca and asked for answers. She was outraged and attacked him, nearly killing him. As he made his way down the mountain, he told Kimahri about Yuna and somehow died going down the mountain. He was never sent, so he remained on Spira, and traveled back in time to Zanarkand through Jecht (who was/is Sin) to watch over Tidus until it was the time that Sin was to attack Zanarkand, and Tidus would really be sent into the present.
2. Not really sure. Go with Renmiri for that.
3. I'm assuming that it's to hide his eye.