How many book and reference should I put into my personal statement?

The main idea for your personal statement is to show that you are enthusiastic about your course and willing to commit. You can refer to as many books as you like but make sure that they all have a purpose. For example, you might have read one book that really interests you to a particular part of the course you applied and you then read another to explore it further. There is no need to write a great list of book names, especially when you haven't read them. This can leave a negative image to the university if they ask you about the book at the interviews.