LEO Missions before Humans to Mars

What type of unmanned LEO missions would you think should be done before a manned mission to Mars? I believe that there should be a mission or two for testing of autonomous rendezvous and a couple of missions for fuel storage and transfer and a couple of tether ("gravity") missions that would scaled up from the TEMPO3 project. Then on the manned side I would do an integrated test of rendezvous with fuel transfer and gravity tether. This may be able to be done with a series of 6 to 10 Falcon 9H class launches. This program I feel could cost as little as $2 billion, as long as you are not paying for NASA's standing army. If you think that this test program has any good points please feel free to expand on it. If you thinks is naive then please tell what sort of test series you would do.