1. Kreia wanted to be free from slavery of the force. She liked the exile because they existed outside of the force, presumably free of "destiny".
2. Yes Kreia was once a Jedi then a Sith, then something beyond both of them. Which is part of what she tries to teach you.
3. Because you gave the order to crush the planet.
4. Think of it like dropping a small pebble in a lake, enough pebbles in the right place will eventually cause the whole surface to ripple.
Well it's all speculation. But it's quite feasable that LA didnt want the armageddon ending where everyone dies to be a possibility. Having variables will always cause a lot of problems in sequels, unless you just ignore them like BG/2 did.