Is being in a "habitable zone" enough to say the planet is habitable for human life? What characteristics would an Earth-like planet need to have to support life? What challenges would we face traveling to and colonizing Kepler-186f, or other Earth-like planets outside of our solar system? Do you think scientists should spend time looking for Earth-like planets before we have the technology to visit them? Why or why not?

No, just because it is a "habitable zone" doesn't mean anything. It could just be an area where things come and go they don't know for sure if it is always a habitable zone until they do more studies on the zone and the area around it. For a Earth-like planet to be able to support life it would need a reliable and large source of water. It would also need a source of oxygen and there would need to be a way to plant food/grow food which would also mean that it would have to have good soil to grow it in. I believe that they would have problems traveling because it is a long distance and it would take a while for them to get the supplies together and by the time they got there they would take even longer on research. Yes it would make more since for them to look at planets and do as much visual research as possible then try to get samples of the planet and eventually work on sending people out to further the research.

Yes because A habitable zone (HZ) in astronomy is a region of space where conditions are best for life to form as on Earth. Planets in these areas are the most likely to have extraterrestrial life. The habitable zone may also be called the "life zone", "comfort zone", "green belt" or "Goldilocks zone".