...not quite everything...What about Squalls ring? It's name is griever, and anyone who's beaten the game should know that Griever was one of the Final Bosses...how did that come about?
Who is Squalls Father?
How in the heck did they all suddenly forget about eachother in the past?
Where did the GFs come from?
Where in the world are they hiding before being summoned?
I for one wouldn't mind a prequel/sequel movie that might explain some of this...
I think some of this may not be answered accurately but strong evidence to support but by what you have just listed it would seem that you would be in support for a prequel rather than a sequel as a prequel would more than likely be able to answer most of this.
Anyway, isn't it best to leave the game as it is and let us think for ourselves and come up with our own conclusions about what happened? Where they related? How did that work? etc. This is the main reason why I don't like sequels/prequels in Final Fantasy as I like the games left with some unanswered questions and so I can come up with my own conclusion or read other peoples conclusions. It gives us a lot more to talk about rather than just about playing the game but also the story behind it all.