You will not encounter any Pokemon as long as their level is lower than the first Pokemon in your party.
you can't
You can get your first pokemon there.
Turn of the game
somtimes you may have to fight a Pokemon in the butt
you won't be able to catch it.
it never explains what happened to it
nothing, you can fight him again.
sorry you have to trade it to Pokemon soul silver
you battle celibe level 5
nothing
nothing really happens when you show her a mime jr.
They will simply gain Exp. You can't breed legendary pokemon.