When you’re davening Maariv, do you say the end of the blessings (Blessed are You, L-rd, who brings on evenings and Blessed are you, L-rd, who loves his nation Israel) yourself, or can you rely on the chazzan and answer Amen? Can you do both, or would it appear as though you were answering Amen to your own blessing, which would constitute a forbidden interruption?
Also, are you allowed to say the blessings and the 3 paragraphs of the Shema (except the possuk rishon) in a quiet voice like the silent Amidah?
You can say the paragraphs of Shema as loud or quiet as you want, so long as you can hear yourself say the words. (Also, be smart that you’re not so loud as to disturb other people.)
You say the Brachos yourself and then you answer Amen to the Chazzan (whether or not you say Amen to Ohev Amo Yisrael depends on your Minhag). It’s quite possible that if you rely on the Chazzan for Shome’a K’oneh for just those final few words of the Bracha that you were not Yotzei, though P’shat probably is that you still were.
In Lakewood we say the bracha and then answer amen to the chazan’s before shema. We don’t say the bracha together with the chazan.
You can say everything as quiet as makes you feel comfortable, as long as you can hear yourself.
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.