Hey Maka, first off, great guide, thanks for the help. Just waiting on my turbo controller for fast and furious. I noticed a possible bug when going for World Champion so figured that I'd share.
You may know that if you quit out of a level with perks activated, you can start another level or repeat the level and keep your perks.
What I found out was that, for me, I could complete the level in offline mode, roll the dice for my character, then quit to the main menu after rolling for my character (before rolling for the AI), then start the game again (by selecting offline mode again, with the same characters as before) and while it would save my score for the level that I just completed, I'd still have the same perks to use in another one.
It might have been mentioned before, but I figured I'd share just in case.