You have to trade.
Yes there were Nintendo events for PokÃ©mon Emerald but not physically inside of the game however there was a Mew that you could have caught in-game that was available on Faraway Island but it was never available outside of Japan since you needed an item called the Old Sea Map before one of the Sailors would have allowed you to board their boat to take it to the island called the Faraway Island.
yu ned to goe to da seafoam ilands.
You won't usually find out where until about a month prior to the event. Try to register with some Pokemon fansites and they'll probably have news about events and suchlike.
No it is like all versions when you beat the elite 4 it tkaes you back to where you last saved (or where it last saved)