Great work! It's amazing the differences between the first and fourth one in such a short time! There are a whole lot of tricks to getting the clay to appear more lifelike, and I think you're on the right path.
One of my favorite (not so secret) tricks for the eyes and cheeks is to apply powdered pastels (real blush and eyeshadow work well too) to the uncured piece. Again, it doesn't take much, but the powders will set right in to the clay when baked and give a really realistic effect. Really subtle brushing of blush on the tip of the ears, nose, a little on the forehead, and of course a little extra on the cheeks goes a long way.
I've been doing portraits for a while (mainly as wedding cake toppers), and this was one of the best little tricks I've picked up along the way