Yes.
how go look for the legendaries!
If you are referring to the old GBA games, then yes and no. You have to beat the Pokemon League in Ruby and Sapphire to get Rayquaza but in Emerald you can get him before beating the Pokemon League. Hope this helped.
all you have to do is beat the Pokemon league 1 time its simple.
what do you mean the elite 4 are in the Pokemon league in evergrande city you should be able to beat them if you have good Pokemon
After you beat the Pokemon league, you can train all your Pokemon, challenge the battle tower, do both, or start over.( i don't recommend starting over)
no to trade between leaf green and sapphire or ruby u must beat the Pokemon league then go to the seven islands and find the ruby and the sapphire gems to be able to trade
no except if its majorly hacked cause they have a super strong fire user
yes,you have to beat the Pokemon league 50 times to be able to go into space
once you finsh the sappfire game you can go lab and get the johto Pokemon to start the johto league now and train them to beat the johto league
use Pokemon on lv 100 with moves that are super effective against each elite 4 member
latias
Yes, you beat the Pokemon League first.