I've never made Feta, but posted my results last week with making a Colby-style cheese using 3 gallons of skimmed milk and 2 of whole milk. Versus the previous 2 batches of full-fat whole milk, my results were about 1/3 less curd.
I've decided to save my skimmed milk for making cheeses like mozzerella and Parmesan,which are intended to be made with lower fat milk anyway.