Having read the question Adding flavor & sweetness to plain greek yogurt, I still have a question. I enjoy vanilla-flavored greek yogurt. I know pure vanilla extract is a very strong flavoring. How much vanilla should I add to a cup of plain greek yogurt? How much Splenda to the same amount of yogurt?
This is a matter of taste. You should experiment and see what you prefer.
Based on these blog entries chosen because they come early in search results for "homemade vanilla yogurt"
you might want to start your experimentation with the following ratios:
On a per cup basis, this works out to about 1/2 teaspoon of vanilla, and 2 1/4 teaspoons of sugar or equivalent.