Well I'm with Ken. I don't hang or press my feta either. After letting it stand over night in the moulds, I then place the cheese into a container and pour over a 12% brine. I have made the brine on either water and whey, I get the same results. The container is almost the exact size of the cheeses, so they don't get overly salty.
I would have said that the cheese would last 6 months, but I don't know about indefinately.
There are lots of threads here in regards to feta. Go back to the beginning and see if you can find the answers your wanting there.