Also, if there is carbon dioxide, oxygen can be made. Outside of the asteroid belt, nuclear power would most likely have to be used. There are advantages and disadvantages to each type of power. On Earth, we are protected by a magnetic field and an atmosphere. Very few have both.
Some planets have very strong magnetic fields that create even more radiation.
Settlements will have to be protected to some degree. Gravity - planets or moons with a lesser gravitational pull than the Earth will result in astronauts having smaller bone and muscle mass, a serious problem if they are to come back to Earth. The closer a planet's gravity is to Earth, the less of a problem this is. Atmosphere - Some planets have no atmosphere. Some have atmospheres that will crush people.