1) I believe she says she first met Jecht 10 years and 3 months. She also says afterwards that that was the day that her father left.

2) I'm sure there was enough time in between jail time and pilgramige for Yuna to ask Jecht about Zanarkand. Or to over hear a conversation between him and Braska and Auron.

3) We can only assume. He was probaly drunk and did something bad.

4) go to question 5 for answer.

5) I have no clue.

6) It was most likely Yunalesca. To defeat sin, a summoner needs to summon the final aeon. To summon the final aeon, the summoner needs to prepare their body and mind. They do this by summoning other aeons. This is why Yunalesca created the the regular aeons. Except maybe anima because all already said I dont know about her.

7) Somebody, probally an al bhed, his Yojimbo in the cave so that summoners could not learn how to summon it and may not be powerfull enough to summon the final aeon. The majus sisters had always ben in the Remiem temple. But since hardly anyone lives in the calm lands, the temple was forgotten and people just stopped going to it. Apparently, Jyscal lived in the Baaj temple and thats why Anima's fayth was placed there. After Jyscal died and Seymore became a maestor, the temple was abbandoned. I guess the sea level rose their afterwards to make it ruins.

8) Belegamine was a summoner that failed to beat sin. Apparently, her final aeon failed to work because she was not strong enough to summon it or she died froma freak heart attack or something after she learned how to create the final aeon since she knows about it when you meet her (I think).She stayed in Spira to train summoners to become strong enough to stop the spiral of death. Note I'm only 50% sure on this so don't completely take my word.

9) Trema was first mentioned in FFX-2. Either Lord Gandoff or Lord ohhaland created the gorge when they defeated sin. Since then it had become the tradition to summon the final aeon in the calm lands.

10) I don't remember that but I will take your word fo it and look into it.

Merry Christmas to you to