What is considered fair game for writing about in a novel?

So basically, I am planning on writing a novel this summer in which one protagonist idolizes Michael Jordan (and eventually makes it to the NBA), while the other looks up to Oprah and is able to fulfill her dream of becoming an Oprah-esque talk show host. Before I get too far in writing however, I am wondering as to what are the legal restrictions on writing about real entities (such as sports teams) and individuals (such as Jordan, Winfrey, and any other famous people). Can I have them utter quotations that they did not say in real life, and if so, what are the risks/limitations in doing so? Can I have them partake in actions-- even if unoffensive-- that may not partake in in real life. Could I get sued? Likewise, if I were to change names but still have them unequivocally speaking about said subject, could I get in trouble? Basically, my question concerns using likenesses in a fictional work. Ultimately, I want to write an entertaining and historically accurate novel, but I don't want to run into legal difficulties in the process. Oh by the way, I live in California, don't know if that matters at all...