2: It's very hard to level up your pokemon to high levels. I suggest you rebattle trainers and take on the league a second time. It might also be a good idea to save a bunch of rare candies on a second game, then make a pokemon hold it while trading.
Hello! I saw you needed help on the new members forum, and I can try to help. 1. The pokemon you want to find with a gba inserted are very rare. You also have to defeat Cynthia before you can find one. I think you might have to get the National Dex too.