1- Nowadays it is best for each person to daven maariv himself and not rely on hearing it from the Shliach Tzibur.
2-Whenever someone is motzei you with a bracha you should always answer Amen. (Although your question as to why its not as if you said amen to your own bracha needs an explanation)
3- Yes. Including pasuk rishon. Its best if you can hear what you are saying, which applies to Shmonei Esrei as well.