I guess it's good to purchase more animals as you won't have to worry about the basic items, such as eggs, milk, bacon and wool. However do note that as you increase the number of animals on your farm, more feed will be required and your barn will be exploding with supplies. To tackle this problem, my advice is to sell away the items that you do not need so as to free more space in your barn, while simultaneously earning profits from the sales (Killing two birds with one stone. Ain't it a good idea? ) Also, expand the number of slots in the animal feed machine to increase production and constantly upgrade your barn to ensure sufficient storage space.