1. Radial velocity, astrometry, transit method, optical detection.
2. Astrometry makes the most sense to me, because they can measure's a star's movement and deduct that from the total mass.
3. The Goldilocks zone is when a planet is a reasonable distance from its home star where it's surface doesn't get too cold or too hot. Which leads people to believe liquid water may exist on that planet.
4. I think the life would be far different than ours because it's immune to different things, so what ever is most common on that planet is what they're going to be use to. I think they're going to be a lot smaller than humans, a lot uglier, and far more advanced than we are. To me they would be said to be smart, because if they do exist, they sure did keep there existence secret for a long period of time. Which is far more than we, as humans, could say about our existence.
5. I do believe in aliens, I just think they're are smarter than humans. Because if aliens do exist than they've been able to keep they're identity secret from humans, who claim to be the smartest species to ever step on earth. Imagine if aliens could prove them wrong! Another reason I think we never see aliens is because they know the human race will want to experiment on them, ask them constant questions, try to learn they're language and ask them about the planet they came from. Even a smart alien would could tired of being examined like a new animal or unique plant. Alien are just plain GENIUSES.