Nothing happen,you will just earn EXP and money.
They don't get sronger, but your Pokemon will get stronger if you battle them a lot.
The Elite Four becomes stronger by itself once you beat them. All their pokemons become about 20 levels stronger after the first time you beat them :)
After defeating the Elite Four once, their Pokemon are much stronger than before, and with new Pokemon. There is no new Elite Four to battle, though.
Yes they do I can tell you from experience.
Beat the elite four again but they get stronger
Yes and No, Yes because its a stronger pokemon, No because his type is not suited for the elite four whether you have one or not you can change that by teaching him various moves.
they might be a bit stronger or weaker but yes
No, you don't have to, But they give you lots of money + exp.I like money.
You will get the chance to defeat the Elite Four.
nothing
You have to level up your pokemon a lot and make them stronger.
You can't. Once you've conquered the Elite Four the first time, they do get stronger, but the strongest one you face is Blue's (your rival's) starter at Level 75.