Ngaire,
I am sorry I am replying so late to your questions, but I was out of town again.
In regards to your questions, information on how Marvin lays out his palette go to
http://forum.portraitartist.com/showthread.php?t=5935&highlight=mattelson+palette
My palette can be seen at
http://forum.portraitartist.com/showthread.php?t=4729&page=3&pp=10&highlight=sorg+ easel
I basically follow Marvin's layout, except on this particular palette on the photo,I used only the gray values. The photo shows the mid value 5 gray that the entire palette is painted in.