routes 49 - 72 ( i think)
the only elite 4 you will face are Lorelei and Agatha, the only real league is the championship fight against Drake on Pummelo Island. It's not a formal league like what Kanto or Johto has.
To sustain the lack of big boss battles there are several character battles against favorites like Brock, Misty, Tracey, etc.
Also to fill up the content, there are 30 islands in total and Southern Kanto as a postgame, which includes another 10 or so islands.