Well you could go to white forest on white and find ghetsis on black go to front of black city
Yo mammas house
yes you have to find all of the seven to catch rayquaza in pokemon white
i have been on several official cites looking for this including Pokemon wiki and serebii they list how to find the seven sages but not ghetesis so i think you cant sorry
they are in caves
you have to find all the seven sages ,beat Cynthia ,alder and the elite four.
Yes at the very far side of it
he only is in Pokemon platinum and Pokemon black and white in Pokemon platinum you see him in jubilife city, and I think maybe at Team Galactic HQ. in Pokemon black and white after you beat the elite four, he is looking for the seven sages. after you find all seven sages he'll talk to you and he'll arrest the 7 sages. you will never see him again after that.
Not too much, go to White Forrest, catch all the pokemon. There is not any other story lines that I'm aware of
An event
you don`t find him. By being spotted far away it meant he was probably in another region
Nothing. Take self satisfaction in a job well done if you didn't have to cheat to find them.
Just do whatever you want! :)