I think your percentage of nofollow is high. A natural link profile is really about diversity. Different types of links (contextual links, image links, video links, sidebar links, blah blah blah links, etc.), different types of anchors (keyword, generic, url) and a gradual/consistent growth in number of backlinks. I don't think you have to try to get as scientific as you did with your proportions - just aim for diversity in every way and you should be ok.