I'm working on a comprehensive History Of Spira, and I need a couple of questions answered.

1. Bevelle started the Machina War, but do we know why?
2. If Shuyin was busted trying to use Vegnagun and executed (along with Lenne), then why is there a sphere of him imprisoned in the gaol beneath Bevelle? Did he try to use Vegnagun twice or something?
3. How and why did Jecht get to Spira? Was he the first dream to cross over? Could any of the dream-denizens have crossed over? Why Jecht in particular? Was this Sin's first appearance in the fayth's dream, and if so, how was Sin able to cross into the dream? Also, since Auron was able to use Sin to cross into dream-Zanarkand, could any unsent have done it, or was it only because of Jecht being the first dream to become Sin?