lol

1. IMO I think Matron only knew that Ultimecia was a sorceress, nothing more. That whole talk was basically a sequence of events that led to the whole story of FF8. Ultimecia possesses Edea, SeeD is born, travels to the future to kill Ultimecia, and Ultimecia travels to the past with her last ounce of strength and possesses Edea again. It's a causality paradox. I know it doesn't make a lot of sense, but suffice it to say Squall was only viewing what started it all (did Squall start it all!?).

2. I always thought Squall never died (sure looked like it like brain death or something). But yeah, LionHart's description best fits my idea here.

3. I think Rinoa's sorceress powers revived him on that spot. In the end, she has Life and Full-Life magic to use.