No you dont have to.
Nope
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.
yes
Yes, you beat the Pokemon League first.
No you don't
Beat them again
yes . raquazas location does not open itself until after you beat the Pokemon league
You cant skip the league, if you want to end the game. You have to beat the league, in order to get the national pokedex. Then you can start trading, to collect all 493 pokemon! hope I could help
You can beat the Pokemon League it is just one of the harder Leagues than in Pokemon Emerald or Diamond.
You need to beat the elite four and then beat the Pokemon league champion
beat the league and he will be gone
There is only one way to beat the Pokemon League. But remember, intense training (for a video game) can help you beat anyone on the game. But, if it helps, the strongest pokemon in the Pokemon League is level 60.