OVKTD: There are different Minhagim. The Shulchan Aruch is based mainly off the Sefer Chassidim that there are 5 bows in the Amidah, with the final one being before the three steps back. Enough people don’t do the fifth (and haven’t for many years) that there probably is some decent Halachic reationale behind it. But yes, it is proper to bow for that too.
About the bouncing thing. There is no source. I have always figured that it stems from the fact that in theory, when you take your three steps forward it is supposed to be right into the Kadosh, Kadosh, Kadosh of Kedusha, especially in the communities where the Tzibbor doesn’t say Nekadesh/Nakdishcha.