fill up your pokedex
nothing
The is nothing else to really do. The seven sages were basically the final mission.
Nothing
You don't.
When you finish finding the seven sages looker comes and tells you about n ps he does not give you the liberty pass
You get TMs. I don't know which ones exactly though.
He goes back to sinnoh
No,you can't. maybe in an event.
After finding the 6 Sages(Ghetsis and N must be in Sinnoh), you go onto your adventure,completeing the PokeDex.
no one knows exactly where but their was a report that he is at a far away place. at the end and your in your room come down stairs and you will find out.
u dont find him he was arrested after battling him in the league
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