What is the meaning of "veha'Shkos"?
Rashi: This is like u'Lehashkos (in order to give to them to drink).
Did they drink from gold Kelim?
Torah Temimah citing Esther Rabah: No - this disgusts a person! Rather, they were fine glass Kelim valuable like gold.
Malbim: Yes.
Why does it say "mi'Kelim Shonim"? It should say 'Meshunim'!
Torah Temimah citing Megilah 12a: A voice from Heaven said 'the Rishonim (Belshatzar and his company) were destroyed due to Kelim 1 , and you are Shonim (repeating their mistake)!'
Rashi: The Kelim were different from each other. This is like "v'Daseihem Shonos" (3:8).
Vilna Gaon: One who drank in a cup did not drink again in it; they gave to him a different cup.
Malbim citing Mahara'a: Other Kelim were attached to the Kelim. E.g. a gold flask of wine had gold cups attached to it. Everyone had all the Kelim that he needed; no one needed to borrow. This shows the abundance of Kelim!
Maharsha (12a): They used Kelim of the Beis ha'Mikdash.
What do we learn from "v'Yein Malchus Rav"?
Rashi citing Megilah 12a: Each person was given wine Rav (older) than himself.
Rashi: It is much royal wine.
Vilna Gaon: It was very dear wine, that only kings drink. They bring much wine to a king, to choose which he wants - so they gave to everyone.
Malbim: Do not say that there were enough Kelim because there was little wine. The wine was great in quantity and quality, so many drank.