How much yogurt? What is the ounces?

The yogurt is being used to add moisture and creaminess to the finished dry curds, so the precise amount can vary according to your personal tastes. I would probably add in at least 1/2 cup of it myself. The recipe seems to call for a single serving container, but even those vary so much by weight and volume that it would still be unhelpful to say. However, I'd start with at least 8 ounces- unless you prefer a drier cottage cheese - and add more if you want it more creamy.