I agree, you're going to want a base on Mars before you land there. No point going all the way there just to spend three days there (like the Moon) so significant living quarters are a great idea. To my way of thinking the best way to build is using the local materials -- either digging underground or building out of rocks. If you were clever, and if you could find a decent source of water, you could probably build a pretty good structure by using dirt and ice. This, of course, requires a lot of fancy robots.

As far as the ship goes, you're definitely going to need a "mothership" capable of entering and leaving Mars orbit (so, a crapload of fuel onboard or else a new engine technology) as well as a lander, so abort capability shouldn't be that big an issue.

The more I think about it, the more difficult a Mars mission seems, and the more sensible it seems to keep on sending robots until we're really ready for a permanent Mars colony (i.e. the point at which it actually makes economic sense).