Thanks for all the help everyone. I've given up with this being allla prima, now I'm just playing with it. That was the whole intention of this anyways.
I'm finding this very difficult to do. Not sure if working from a computer monitor makes it more difficult, as well as my inexperience of mixing skin tones (either get everything too light or dark) but I've learned so much from doing this piece.
The colours so far that I've been using are, red iron oxide, raw umber, yellow ochre, titanium white. I haven't been really worrying about what is warm and cool yet. I'm just trying to get tonal values down, then I want to cool where needed. I'm not sure if this approach is the best, but its what I've ended up doing as a result of all the mistakes I've already made.
It is amazing all the subtle variations from cool, warm, light and darker in skin tones - mind boggling.
Also what bugged me is how orange everything is. I just bought some veridian today and I'll re-adjust in later stages.