After league, trade with a FR/LG or Colosseum or XD with full completion on any GBA game from the list.
Yes
http://pokemondb.net/pokedex/national
beat the hoenn pokedex and go to prof.birch
you don't need a national pokedex to trade from ruby to leaf green. You have to get the gems the sapphire and the ruby in order to trade from leaf green to ruby. These are found in leaf green. (:
Cheatt
You can link and trade Pokemon with Sapphire and Emerald Versions. If you want a national pokedex, trade with leaf green version
after you beat the elite 4 you should automatically get it if not see professor oak
After getting the national pokedex get the ruby and give it to celio. he will give you the rainbow pass for islands 4-7.
catch all Pokemon
The original Pokedex is given to the player by Professor Birch. After the Pokemon Ruby trades with LeafGreen or FireRed the National Pokedex will be unlocked.
yes you do because i tried it without a national pokedex and it didn't work but once i traded pokemon fire red worked perfectly
the kanto pokedex YES national not sure but i think you have to trade from ruby or sapphire or something