Difference between 说话 and 话说?
You need to differentiate them as "话说" carries a different meaning. It is used when people want to start a topic. It is very commonly used in ancient novels, where authors always speak as a storyteller and use "话说" to begin the story. In informal conversations someone may also use it now (actually I used to say it many times), a little like "by the way" in English. 

My personal opinion is that, practically you'd better avoid using "话说" in your writing when you are not a high level Mandarin writer, because I think "话说" is related to a specific writing style. You may use "话说" in informal conversations.