Yes, as MadisonS pointed out, you will not get "double credit" if you pass the AP exams and also take (and pass) the CLEP exams. It is one or the other. But if you are not confident in how you might have done on the AP exams and you want some certain credit, go ahead and take the CLEP exams.
I have heard of people using the AP books in their study preparations for the CLEP exams. Have you already looked over the exam descriptions on CLEP's website? If not, definitely do this as you will want to see what material is going to be covered on the exam. Also, the description should contain some textbook resources and possibly some online resources to use in preparation.
