I believe required amount for the 4 Kossos is deemed to be 3.3 fluid ounces albeit there is an entire gamete ranging anywhere from 2.5 to 5.1 fluid ounces.
For 1st cup on a Friday nite, the required amount generally is deemed to be 4.42 fluid ounces. Notwithstanding, if the Ba’al haSeder is being Motzi everyone else’s Kiddush, then only he requires 4.42 fluid ounces, and everyone else only requires 3.3 fluid ounces.
Furthermore albeit Kiddush on Friday nite is 4th commandment, yet the 4th commandment is to announce/sanctify Shabbos, but not necessarily on wine, so even iof one did end up making Kiddush on 3.3 fluid ounces, one would probably be Yotze anyways.
Furthermore, according to Rambam [whose birthday is coming up this Friday, since he was born on Shabbos Erev Pesach] even Havdolo after Shabbos is part of this 4th commandment, but no-one seems to mention having a larger 1st kos on Moztei Shabbos.
Another question:- Do we chant Sholom Aleichem & Eshes Chayil this Friday evening prior to Kiddush on 1st cup?