yes you can only after you beat the elite 4
No, you cannot migrate GBA Pokemon to Pokemon Black/White.
You cant. you can only send to pokemon white
Yes
Migrate from Pokemon Sapphire to Diamond then Diamond to Black/White
You can't get a skitty in Pokemon white unless you migrate it from another game.
Yes. After you beat the main story, you can migrate from daimond, pearl, platinum, heartgold, and soulsilver versions to black and white
First you have to migrate the Pokemon to diamond(have to beat elite 4) Then you trade the Pokemon to Pokemon white
You have to migrate mew from generation 3 as of now.
No, items can't be migrated, but if you migrate Shaymin across, take it to Lacunosa Town's Pokemon centre, a woman inside will give you the Gracidea.
Not directly. You have to migrate to diamond pearl platinum heartgold or soulsilver first and then after you beat the elite 4 in white you can connect 2 da systems to migrate from diamond pearl platinum heartgold or soulsilver over to Pokemon black or white.
Pokemon Black and White are not compatible for trading with any of the other previous games.
with a copy of diamond, pearl, platinum, heartgold and soulsilver make sure you have 6 Pokemon in the PC in those games and head to the pokeshifter in Pokemon black and white and you can migrate those 6 Pokemon from the games listed above, see serrebii.net for more details.