Thank you for your question. Without photos, it is very difficult to provide you with a good solid answer to your inquiry. The potential reduction in inches from liposuction of your waist would definitely be determined by how large or small you are to begin with pre-operatively. Please be certain to schedule a consultation with a board-certified plastic surgeon when you are ready to move forward.
It is impossible to say. 5" is a pretty extreme goal. My best advice would be for you to schedule a consultation with a board certified plastic surgeon to be assessed in person. He or she should be able to give you a more accurate response.