How and when am I able to use final limit breaks? I am on level 3 limits with Cid, aquired his final limit break, the Highwind today, yet he's not able to learn it. How do limit breaks go up in level, and how can I check how long it will be before he can learn Highwind?

As some of you may know, I'm going to be facing Sephiroth fairly soon. How many HP do the three (or is it two, I remember three) parts of Sephiroth have?