1. You should pick out a ninja you like the most and make that your main and level him/her up more than the rest. 2. You should have a second favorite character to level up close to the main's level. 3. You should just focus on a few of your favorites and then later level up the others. 4. You don't need more than 12. I have 12, but honestly i focus on 10. Around half are above lower blue belt. 5. You should be careful with your karma points, because you will need them for a lot of stuff. 6. Enjoy!