Is it okay to base characters for my book on a famous entertainers, if I do not actually use their names?

You cannot use the names/images/voices of other people for your commercial purposes unless you have their permission. Everyone has a right of publicity to prevent that. The right of publicity varies from state to state, however if you are going to be offering your book in all states then you must comply with the laws of every state. There are exceptions that allow use in certain situations, but again this varies from state to state. In general, it is not a good idea to use someone else's name for characters in your book even if you slightly change the name. You can still get in trouble even if you are not using their exact name.