All of your sentences are correct. In each response, although "do" is not necessary, it does place emphasis on the statement. "I have money", and "I DO have money" mean exactly the same thing. I put "DO" in capitals to emphasize the written statement. In verbal communication, the person would most likely stress the word "DO" by stating it louder than the other words in the sentence. Many people use it all of the time. Many others use it only for emphasis, often when they are annoyed at something: Do you have money? Yes, I have money. I thought you told me you didn't bring money. I just told you, I DO have money! In this exchange, the second time the person says they have money, they want emphasis because the first time they said it, the person asking the questions apparently did not believe them!