The whitewater, while awesome, is not that hard. If you are a IV/V kayaker you have the skills to run it. There are a lot of online resources, I was going to post some, but a google search of self support grand canyon will give you a lot of great things to read.
At the end of the day it is really just a matter of winning a permit. Winning in the main lottery is hard. Picking up cancellations, especially cancellations close to the put in date is a little easier. Also, as someone said, if you are willing to go in winter you will have a lot less competition for dates. Good luck - it's one of the best trips you can go on.