QuartZ coached my on bust painting...
He and I use Liquitex brand acrylic paints. They come in a tube, break down with water, and blend wonderfully (think of your line between the black eyes and the whitish face). You can thin them down and apply with a brush and blend out all brush strokes, or you can airbrush them. They're found at craft stores like Michael's.
I use Testor's Clear Flat in the rattle can. Goes on very thin, dries to the touch (depending on humidity) in 5-15 minutes, and is essentially impervious to the acrylic paints (i.e. you do a layer of paint, spary the Flat, and that first layer is permenantly locked in -- you can paint right over teh Clear Flat without effecting the underlaying layer).
I've not heard of using Future for the purpose of sealing between layers. Though I am VERY familiar with Future, and do use it for many other applications. No offense to the person who suggested it, but all I see is 'negatives' with this. It will go on a bit thicker than the Testor's. It will leave less "tooth" for your next layer of paint to grab (military modelers use it prior to decaling because it leaves a wonderfully smooth surface for decals to adhere to), and it will require amonia (I believe) to clean your air brush (water will clean the brush if you use acrylics). Not to mention that you have to haul out the airbrush in the first place (opposed to a ready-to-go rattle can).
If I were to paint this subject, I'd mix my base flesh tone (which is generally too white to begin with as "tanning" coats are added later) to a point where it looks like your skin does when you peel off a band-aide. Make sure it still is "fleshy, though -- not pure white. I'd do one or two thin base coats then seal it with the Flat. Then I'd add whatever effects are needed (mottling, veining, etcetera) and seal it again. Then I'd add one or two more coats of the base flesh color, and seal it again.
At that point I'd step back, examine, study, think, ponder... Then I'd start the true art work -- finessing it, adding details, "massaging" it until its just right. Sorry this last bit is vague, but this is where subjective, artistic talent takes over and overrides the more "mechanical" or "procedural" steps.
And enjoy yourself. Bust painting is tricky, but is really fun. If you're getting frsutrated or not having fun with it, something is probably wrong. Step back and reapproach it later.
Man I want to do one of these now.