I believe the medifast coaches have gone through medifast completely and have lost and kept off all/most of their weight...I know mine started Medifast last year and has kept off about 60 pounds...Not 100% sure though as to the requirements but I'm pretty sure they've all gone through the program and are success stories..
You need to have at least been on the program for a certain amount of time, before you can become a coach, so you can help explain the program and let your clients know what to expect.
You will make your money on commission. It is not like a regular job. It is kind of like Multilevel Marketing. You also get people to sign up under you as a coach. You have to find your own clients.