1)    At the end of the sentence “Oseh Shalom” we say “Ve’imru Amen!”. Even though we are praying quietly and no person can hear what we are saying, we say this to the angels who are listening to the prayer. (Kaf Hachaim 123)

2)    One of the reasons that we take three steps backwards at the end of the prayer is that Nevuchadnetzar merited to reign over the entire world and to destroy the holy temple in the merit of three steps that he took to honor Hashem, and we therefore also take three steps, and it is for this reason that immediately afterwards we pray “Yehi Ratzon Sheyibaneh Beis Hamikdash” (May it be Your will that the temple will be rebuilt!”). (Mishne Berurah ibid)