1. No
1.1. According to the Drake Equation that is often associated with the Fermi Paradox, there is a very high probability for aliens to visit us at least once. However, there are no confirmed reports of this.
1.1.1. Of course, there are conspiracy theories involving the U.S. government shrouding information on aliens, but the chances are very slim, considering most UFO (unidentified flying objects) are not what they seem as.
1.2. It is also possible that only humans and other forms of life on Earth made it through the "Great FIlter", making us the unique form of life.
1.2.1. This means that us humans survived a great disaster in the past that has swept large amounts of species.
1.3. Messages sent out, such as the Arecibo Message, have not been replied.
1.3.1. Though it is possible that we couldn't understand the responses that the aliens are giving out, the chances are minimal.
1.3.2. However, Voyager 2 is carrying a message and if some alien passes by, they would hopefully know where to look for us.
2. Should we look for them, if we assume that aliens do exist?
2.1. Yes
2.1.1. Aliens may prove to be vital to further research to how life forms.
2.1.2. If the civilization is advanced enough, we may be able to take some technological creations from them.
2.2. No
2.2.1. The aliens, if we meet any, may exhibit xenophobia and could be hostile to all of us.
3. Yes
3.1. There are approximately 100 billion billion Earth-like planets in the Milky Way.
3.1.1. There is no reason is to why a planet that could support couldn't exist outside of Earth.
3.1.2. The Drake Equation, for instance, gives a high probability for the existence of life beyond our home planet.
3.2. Water exists on numerous planets and moons, and could support life as we know it.
3.2.1. Some of these planets or moons include Europa, which has a thick layer of ice on it.
3.2.2. Others, such as Kepler-186f, are Earth-like planets within the habitable zones.
3.3. It is certainly plausible that aliens do exist, it's just that they are not advanced enough to go into space travel.
3.3.1. Stephen Hawking once said that life forms may exist beyond Earth, but life forms that have developed into advanced society will be hard to find, if there are any.