David,
for what it's worth: I always undercoat in acrylic paint first. I use Testors "skin tone shadow" mixed with a touch of white to begin (I vary the white depending on the skin tone light/dark I'm going for). As you may well know, a smooth consistent base coat is paramount in painting with oils.
I use a very abreviated oils pallet much as Bob does. I use Raw Umber, Cad Red, Yellow Ochre and Titinium white. I ususally start with the shadow or mid-shadow tone, adding white for the highlights and a bit more umber for the deepest shadows. A touch more cad red is added in the darkest shadow color for the cheeks and lips as needed. I have been known to use straight raw umber for some of the deepest shadows. Never straight white for the last highlights, always a very light flesh, this then is used for the "whites" of the eyes as well. I always work wet-on-wet. I probably "over blend" as Bob mentions, but it seems to work for me. I think it's all in what your comfortable with. HTH, good luck, post some progress as you start to get your feet wet!
If you get a minute, my web site (link in my signature "www") does have some pictures of a flesh tone pallete that I used on one of my projects, the "Barbary Brigand" Latorre Pirate bust. This might help give a better idea of what I'm trying to explain.
Jay H.
OKC