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- One should stand when answering Barchu, however, one may sit after one said Barchu even before the Shaliach Tzibbur repeated the Barchu out loud.
- According to Ashkenazim, the accepted minhag is to bow during Barchu.  According to Sephardim, the shaliach tzibur must bow when saying Barechu but the congregation does not need to bow, though many have the minhag to bow slightly. 
- If one continued Seudat Shelishit into the night (past Shkiah) one should still say Retzay in benching, even if one answered Barchu. However, if one already said Maariv, one should not say Retzsay in benching. 
- If one is saying Mariv/Arvit to oneself some say that one should say a Britta (see end) in place of Barchu.  However, many hold that one should not say it with Hashem's actual name but rather one should say Hashem. The text of the Britta is: אמר רבי עקיבא חיה אחת עומדת ברקיע ושמה ישראל וחקוק על מצחה ישראל עומדת באמצע הרקיע ואומרת "ברכו את ה' המבורך" וכל גדודי מעלה עונים ואומרים "ברוך ה' המבורך לעולם ועד" .
- Sh”t Beer Moshe 1:2 based on Taz 146:1
- Beiur Halacha 113:3 s.v. HaKoreh, Kol Bo 8. However, the custom of the Gra (cited in Ishei Yisrael pg. 160) was not to bow
- Shu"t Ohr Letzion 2:15:13, Yalkut Yosef (57:8-9, vol 3 pg 421). See there where he writes that it is preferable for the congregation not to bow and Rav Ovadyah Yosef's practice was not to bow at all.
- Sh”t Beer Moshe 1:5
- Chida in Tziporen Shamir 2:26, Ben Ish Chai (end of Parshat Vayigash), Kaf HaChaim 50:9
- Sh"t Yabia Omer 2:4, HaTefillah VeHilchoteha 28:9