About the stravy (dishes) of Sviat Vechir, their number and their Lenten nature.  The dishes served on Sviat Vechir are vegan (no meat, dairy or egg) plus fish.

From Kylymnyk, Volume 1 (Winter), pp. 20-21, my very rough translation

Why are twelve dishes prepared on this night? Why are these dishes Lenten?

I have come to believe, based on my extensive research, that there are twelve courses because, in the course of a year, “the moon circles the earth 12 times.” Therefore, one dish is dedicated to each month. Secondly, on Bahata Kutia (Sviat Vechir), dishes must be prepared incorporating all the fruits and vegetables that the household has produced in the past year. This allows the household to receive the god of the harvest and the holy souls of their ancestors, and to share this bounty with them. Having tasted all of these dishes, the god and ancestors will provide an even bigger harvest in the coming year.

The dishes on Sviat Vechir must be Lenten because on this night the ancient Slavs, our ancestors, brought to the god of the harvest––the sun––a bloodless sacrifice from all of their useful plants. These were magical acts––to give the god this rich abundance of the “Bahata vecheria (rich supper),” all of their vegetable wealth. The god of the harvest would see this abundance and grant an even better harvest. But, along with the god of the harvest, the “god of livestock” (who was later called “Veles”) would observe the proceedings of this evening. Therefore, on this evening, not a single animal should experience even the slightest harm, nor should there be any blood.

"The order or the serving of the dishes is approximately this:
1. Kutia
2. Horokh (peas) and kapusniak (two dishes consumed together)
4. Borshch with mushrooms and fish
5. Holubtsi
6. "Ryba kholodzhena" (? fish in aspic)
7. Fried fish
8. Varenyky
9. Mlyntsi (eaten together with the borshch)
10. Kasha (specially prepared)
11. Pyrizhky
12. Uzvar

The dishes are not the same everywhere, there are many changes and specialties; also, the order of service--the alternating courses--are not identical everywhere."

He also notes that the 12 dishes represent the 12 months of the year, and that in some areas 17 dishes were served (although he doesn't say why).

Whether alcohol is allowed on Sviat Vechir. This is what I found in Kylymnyk, Volume 1, page 30.

По першій ложці куті, господар наливає чарку горілки, запіканки, вишнівки чи сливняку, а в давні часи – меду, – підносить чарку вгору, сам встає і повторює попердні слова:

«Дай, Боже, царство небесне всім померлим, у небі панування, а нам щастя, здоров'я і довге життя!»

Чарка обходить усю родину по черзі.

After the first spoon of kutia, the master of the house pours a small glass of horilka, zapikanka (?), vyshnivka (cherry liqueur) or slyvniak (plum liqueur), or in earlier times, mead. He raises the cup high, stands and repeats the preceding words:

"Give , O God, the kingdom of heaven and dominion there to all who died, and to us happiness, health and a long life!"

The glass is passed around the family, to each in turn.