How to take the steps back and bow by Oseh Shalom of Kaddish:
After the completion of Kaddish [prior to Sim Shalom] the custom is to take three steps back and then recite Oseh Shalom Bimiromav, just as is done at the conclusion of Shemoneh Esrei. [One is to turn and bow his head first to the right when saying Oseh Shalom, then to the center when saying Hu, and then to the left while saying Yaaseh Shalom Aleinu, and then to the center when saying Veal Kol Yisarel. One is not to begin saying the words of Oseh Shalom until he completes taking three steps back. Seemingly, one is to move his right foot first and only then his left, just as he first bows to his right.]
To which direction is a lefty to bow first and which foot does he move first by Kaddish?
Seemingly one who is left footed, he is to take three steps back with his left foot first. Likewise, one who is left handed should first bow to his left.
 Admur 56:8; Michaber 56:5; Terumos Hadeshen 13; This applies by all Kaddeishim: Radbaz 1:139; Mamar Mordechai 56:2; Kaf Hachaim Falagi 13:20; Yifei Lalev 56:11; Ketzos Hashulchan 16:7; Yabia Omer 5:9; See Piskeiy Teshuvos 56:10; Nitei Gavriel 41:8
Other opinions: Some Poskim rule one is only to take three steps back by Kaddish Tiskabel, and not by any other Kaddish. [Terumos Hadeshen ibid; Mateh Yehuda 56:2; Shalmei Tzibur p. 84b; Kesher Gudal 8:20; Chesed Lealafim 55:15; Od Yosef Chaiy Vayechi 6; Shulchan Hatahor 56:6; Kaf Hachaim 56:36]
 Source regarding bows by Oseh Shalom: Sefer Haminhagim p. 16 [English] and custom of Rebbe; Implication of Admur 56:8; that it follows the same customs as Oseh Shalom of Shemoneh Esrei, which includes the bows to the right and left as ruled in 123:1; Ateres Zekeinim 123 in name of Mordechai; Chayeh Adam 30:5; Rivivos Efram 1:113; Nitei Gavriel 41:8; See Piskeiy Teshuvos ibid
Source regarding bowing first to right: Sefer Haminhagim p. 16 [English] that we bow first to the right, unlike by Shemoneh Esrei and so was the custom of the Rebbe [See Admur 123:1 for the opposite order regarding after Shemoneh Esrei, that one first turns to the left, which is to the right of the Shechina which is opposite him; See Piskeiy Teshuvos 56:10 footnote 122 that although Kaddish is similar to Shemoneh Esrei in terms of many of its customs, nevertheless, perhaps it is not considered like actual Shemoneh Esrei in this regard that we view the Shechina as opposite him to his left, and hence we first turn to the right.]
Other opinions regarding moving head: Some Poskim rule it is not necessary to bow the head like after Shemoneh Esrei when taking three steps back by Kaddish. [See Ketzos Hashulchan 16 footnote 17 that the order of bowing applies only by Kaddish Tiskabel; See Piskeiy Teshuvos ibid; Practically, however, our custom is to do so by all Kaddeishim.]
Other opinions regarding where to move head first: Some Poskim rule that one is to move the head first to the left and only then to the right, just as we rule by Shemoneh Esrei. [Possible implication from Admur ibid who writes “Like Shemoneh Esrei” thus implying to bow first to left just like by Shemoneh Esrei; Ateres Zekeinim 123 based on Mordechai that we first turn to left also by Kaddish; Beis Baruch on Chayeh Adam 30:5; Rivivos Efram 1:113; Nitei Gavriel 41:8; See Piskeiy Teshuvos ibid] To note, however, that the Mordechai refers specifically to Kaddish Tiskabel. In defense of the Chabad custom, perhaps we can suggest that ideally we should always torn to the right, as is the Halacha in all matters of precedence [Maharil in name of Orchos Chaim, brought in Beis Yosef 123, based on Yuma 55b that all turns should be done to the right] and it is only regarding Shemoneh Esrei where the Halacha is that we are standing before the Shechina, that we change this rule and bow first to the left. However, by Kaddish, there is no such Halacha that makes it considered as if we are standing before the Shechina, and hence we cannot swerve from the general custom of always turning first to the right.
 Admur 123:1 and M”A 123:2 regarding Shemoneh Esrei and there is no reason to differentiate between Shemoneh Esrei and Kaddish in this regard, as concludes Admur 56:8 “As is done by Shemoneh Esrei”; Beis Yosef 56 in name of Terumas Hadeshen 13 regarding Shemoneh Esrei; See Piskeiy Teshuvos ibid footnote 121 that seemingly this is the novelty of the words in Admur ibid “As done by Shemoneh Esrei”
 This corresponds to our custom to bow first to the right by Kaddish, and the same would apply regarding moving the foot, as explaine din the previous footnotes. I, however, have not found anything explicit in the Poskim or Sefarim on this matter,
 See Tzemach Tzedek Orach Chaim 4:6 and 5:8 regarding Netilas Yadayim, and based on Admur 183:7 that a lefty is to hold the Kos Shel Bracha in his left hand; 651:14 that a lefty is to hold the Lulav in his left hand; See Rav Ginzberg in Haaros Ubiurim 783 p. 74; Sefer Dinei Iter p. 43-46 and p. 141 [that an Iter should bow like everyone else, however looking at his reasons and sources, his ruling is not concrete.]