(1) Further to your comments about "I am not a Chacham", the Rashbam (DH "Visadarna Ana") refers to a R. Yitzhak. Is this the Rashbam's teacher? Is the Rashbam making some reference to his (the Rashbam's) own learning? Or does it refer to some other R. Yitzchak?
(2) With regard to all of the various kiddushes discussed in these pages of the Gemara (Friday night, Saturday, Yom Tov, Havdalah), does it make any difference if Kiddush is made on grape juice instead of wine? Is the alcoholic content of wine an important factor in the mitzva? Does the answer vary by which kiddush is involved?
(1) Rabeinu Yitzchak, cited by the Rashbam, was the teacher of the teacher of Rashi. When "Talmidei Rabeinu Yitzchak" (the students of Rabeinu Yitzchak) are mentioned by Rashi or Rashbam, it means that Rashi or Rashbam saw the writings of his students. (For example, see RASHI in Shabbos 10b, DH Mishkal; Shabbos 59b, DH Trei; Megilah 26a, DH Hu; Gitin 36a, DH b'Shevi'is.)
(2) We will send you an answer to your second question soon.