This is a split board - You can return to the Split List for other boards.
1)From what I heard, you can start trading pokemon or pokemon eggs into HG/SS as soon as you get your pokedex. ( could be wrong)
2)I think thatyou get the national dex by seeing all 250 pokemon.
Again, I could be wrong. Maybe someone who actually has the import version could give a more elaborate and correct answer. Sorry...