1) The Shulchan Aruch rules (422:6) that one must recite Hallel while standing. One should not sit or lean against a wall, table or lectern while reciting Hallel. The only time Hallel is recited sitting, is at the Seder on Pesach night, as the Rabbis did not want us to have to go through the trouble of standing at the Seder table to recite Hallel. On all other occasions, however, one must stand during the recitation of Hallel.
2) A mourner, God forbid, does not recite Hallel during the first week of mourning. Therefore, a Minyan praying in the house of a mourner should move to a different room for the recitation of Hallel; alternatively, the mourner himself should move to a different room when the Minyan recites Hallel.
3) Chacham Ovadia Yosef, in his work Chazon Ovadia (Laws of Chanukah, p. 300), records a tradition to recite a certain text after the completion of Hallel as a means of earning long life, and this text appears in several editions of the Siddur. First one recites the verse (Bereishit 24:10), "Ve'Avraham Zakein Ba Ba'yamim Va'Hashem Beirach Et Avraham Ba'kol" ("Avraham was old, advanced in years, and God blessed Avraham with everything"), and he should have in mind the name of the angel Zevadya. (Zevadya is a name that appears in the Book of Ezra, 8:8 and 10:20.) Thereafter, he should recite, "Yishmereni Ve'yechayeni Kein Yehi Ratzon Mi'lifnei Elokim Chayim U'melech Olam Asher Be'yado Nefesh Kol Chai Amen Kein Yehi Ratzon" ("He shall protect me and sustain me; so may it be the will before the living God and King of the world, in whose Hand is the soul of every living being; Amen, so may it be His will").
