3* Water also appears to be present on the moon[0]
4* Is that enough? We don't know, we've yet to do any centrifuge habitat experiments with small mammals
5* oxygen is so common, CO2 has the advantage of being gasseous, but silicates, aluminum and iron ores are the rocks you can't throw a rock without hitting and has the advantage that you only need to process a millionth the volume to get an equivalent number of moles to martian CO2.
Zubrin does a good job of outlining why Mars is better in his book "The Case for Mars.". He's thinking underground structures on Mars with solar panels and some pressurized agriculture up top.
Mars had much less harsh living conditions than the moon and having water and CO2 around makes living off the land, at least partially, a lot easier than on the moon. The delta-v to get to the moon vs. Mars isn't much different. Getting out of Earth's gravity well is the hard part.
4* Is that enough? We don't know, we've yet to do any centrifuge habitat experiments with small mammals
5* oxygen is so common, CO2 has the advantage of being gasseous, but silicates, aluminum and iron ores are the rocks you can't throw a rock without hitting and has the advantage that you only need to process a millionth the volume to get an equivalent number of moles to martian CO2.
[0]https://en.wikipedia.org/wiki/Lunar_water