Meet Lisa. Lisa works at our booth at Knit City every year. She's great.
Meet Lisa's Sweater. Lisa's Sweater is also great, though it does not work the booth at Knit City.
Lisa knit her Sweater using two skeins of our XL sweater yarn, the stuff that's intended for toddlers sweaters. Because here's the thing that Lisa realized: a 6-year-old is approximately half an adult, as far as sweater quantities of yarn are concerned. So by alternating skeins every row, she was able to make the stripes work and create an adult-sized version of this beauty.
I know you have questions. The answers are: Flax Light, medium, yes, and definitely yes. For more details, see Lisa's Ravelry page here.