Nothing. Red just disappears and doesn't come back. You can always make Red reappear by beating the Elite 4 again.
Then just go back to the place where yu saw him
nothing
With Pokemon.
Nothing.thats it
Pikachu
Nothing...I think you might be able to obtain Kyogre but I don't recall anything else :)
go to prefacer.oke then you get one stear pokemon
You finish Pokemon heart gold after you beat red.
beat the Pokemon luegue then go to the Pokemon centre
Yes
They are still in the Pokemon league
Yes.
you gp to seafoam islands