Berakhot 14

Can one talk in the middle of hallel or megila? Can one taste food on a fast day? Can one greet someone or deal with things before praying in the morning? Can one stop to greet someone in between the words "is our God" to "truth"? Why? Do we say the entire third paragraph of shema at night or only part? Which part? Why? What is the significance to the order of shema? The gemara quotes a braita that tells a different answer than the one given in the mishna. Does one put on tefillin before or after saying shema? The gemara deals with this question by bringing sources and stories that seem to contradict and tries to resolve the contradiction.