By the time you even get to Mars, its very unlikely your body would even be able to handle the turbulence of the ship's entry into the atmosphere even with it being as thin as it is. Bone loss and muscle degradation in space is inevitable if the trip is close to 5 years. People at the space station have to be carried out in a stretcher after landing on earth, and they are only limited to a few months there at most. Add the fact that the soil is loaded with perclorates, self sustaining would be very unlikely if not impossible at this point with our best tech.