The propulsion system from Earth to Mars could just be a scaled-up version of the systems we've been using to send probes to Mars for decades.

Yes, it would be wisest to send at least two trips, so that equipment can be ready for the crew when they arrive. (Especially if you're making return-trip fuel from local resources.)

Radiation is a problem for a manned mission to Mars, but I understand the numbers work out to less lifetime risk of cancer than smoking. (So send former smokers without any cigs and you've improved their expected lifespan.)

Take a look at http://en.wikipedia.org/wiki/Mars_Direct and its descendants. Many of the problems have been solved, with an expected 10-year timeline.