Much Of The Key "Case For Mars" Stuff Is Onlinee
http://www.nw.net/mars/marsdirect.html
Many of your concerns are major barriers. That is why Mars is such an important next step. You don't have to ship massive amounts of resources when you can live off the land and the gravity is as close to Earth's as you can get on a world we can live on with near term technology.
Regards,
Mark