Actually, every game before B/W I've trained only my starter, pretty much. I usually had a backup or two, but mainly relied on starter and pokemon I recently caught to get me by. Then I had many legendaries on my team! However, on this game, I'm equally training a full team of six Pokemon which explains why it's taking me so long this time around, but it's much more rewarding. The lucky egg is really helpful, especially in the story line. Put it on, go against a huge group of trainers (mainly Plasma) and you can easily get a ton of level ups!