Just started and have some questions

[TheSpoonyBard]

I've just started to play FFVI as I need something to do during the Christmas holidays and I have a few questions regarding the game.

1) Who is the main character, Locke or Terra? Or does this game not have a main character?
2) Which characters should I focus on leveling up? I looked the manual and saw them all and I was quite taken aback by the sheer number of characters in this game. Surely not all of them are worth training all the way?
3) How do Limit Breaks work on this game? I assume they go under a different name, but I'm sure you'll know what I mean.
4) How long will I have to wait before I obtain my first Esper?

Please keep spoilers to a minimum, or mark them. I want to be able to play the game through at least once without having anything spoilt. Thanks.