We can get other regions starter Pokemon if we defeat the battle tower
Nothing.
Nothing
you cannot ever beat the battle tower. but if you have completed the sinnoh pokedex then the battle tower will help you complete it. you can battle at the battle tower as long as you want.
nothing you just go back to the reception counter
You win? Once you beat the Elite 4, you can go to the Battle Area (prolly called something else) and there you can compete in the Battle Tower or do some training/Pokemon hunting in the areas of the zone.
At the fight area (after you beat the Pokemon league)
Yes.
there is no battle frontier in Pokemon pearl,but there is a battle tower. you can go there after you beat the elite 4
beat it again. nothing will happen
to get bp (battle points) you have to beat people in the battle tower.
after you beat your rival at battle tower he will reappear every so often
you have to go to the battle fronteir after you beat the game