Any of the first three sai brushes listed in my FAQ can acheive the different looks in these palettes. It's merely up to preference which works best for you. I also had my stabilizer at about 13 when I did this, if that helps.
Hmm well I suppose it depends on how the hair colors are layed out. If it's like different streaks it's easy to separate the colored strands, but if if it's a gradient it's important to make sure to convey the subtle color changes and mixing of hues. It's a little more complicated but totally doable.
So I dont mean to be a pain, but i have really bad eyes and im having a hard time seeing these do to the lighter background that what you normally use, any chance you could darken it? Either way its another great set and I am ever so amazed at your color choices! I am so loving that second purple :3