I've read through the CoS module, and aside from the Wizard of Wines, no one seems to be farming. There are mentions of two hunters in Vallaki, and a single fisherman there as well, but nothing else that I noticed. Wine isn't that high in calories, so the question is, if there are no other farms, how are the Barovian people getting fed?
Very early on in the supplement, under the section describing Barovian culture, myth, and society it states that all Barovians are expected to contribute in a variety of ways:
Barovians live within a closed ecosystem. Every Barovian adult is expected to learn a trade or serve a function. Barovians stitch their own clothing, craft their own furniture, grow their own food, and make their own wine.
So technically, they're feeding themselves. In addition (spoilers):
The Wizards of Wine winery provides all the alcohol to everyone free of charge.
I would imagine that there are farms (not shown on the map) that bring food into the Town of Barovia to trade for the goods and services available in the towns. Also the Barovians could be quite adept at hunting for their own meat, fishing in the river, gathering edible plants, mushrooms, berries, and fruits. As far as I remember there is a windmill that plays a part of the story, so presumably some wheat is being grown and the details are just excluded from the module.
Funny they write it off as saying they make their own food, furniture and clothes.
Barovia & Vallaki: 1-4 adults + 1d8-1 children, meaning up to 11 people in one house. Neither of these two settlements have a controlled wood resource or enough land to produce enough food to be able to daily feed the max (much less min) of people in a single house. Krezk has enough trees on the inside to have enough wood to make furniture, and maybe have an orchard or two. In other words, there is no possible way the people can be self-sustaining.
To make it realistic:
There are hunters that hunt in the woods, they mostly hunt wolves but I imagine they hunt other creatures as well. There have to be fortified farms around that supply the settlements in their area with the vegetation needed for both food and textiles. Then there needs to be wood, so woodcutters have to be able to fight off attacks or be guarded when in the process, then a sawmill by a river to properly cut the logs to be used for construction, and firewood can be gathered from the pieces of wood they cut off the main log of the tree. Each household keeping some animals like pigs, sheep, and chickens sounds right as long as they raise them and harvest only when they have the ability to replace what they slay, or take eggs from in the chickens case.
As far as I remember Strahd "hibernates" for centuries at a time. So it allows the population to grow (well as far as his loose spawn and the werewolves allow) for a time.
I'm not sure how much blood must be consumed and how often they need to feed. But if they kept enough souled humans they could almost drain them dry once a day and use magic to restore their health, keeping them until they age to death. Also magic can be used to keep blood as fresh as it was when still in the body so keeping cattle and draining them once a day to store extra blood. These are just a few ideas.