Deneen has posted a great tutorial on how she made her version of the sweater.
Check it out!
Oh, and she's starting another one (for herself I think), for the CAL...
Your stitches will look different if you spiral--you could do either of those options--make the seam down the front a design element, or move the seam to under the arm. I think they're both good ideas! A third idea, is to see how you like the change betweent the spiraling and working in rows, and see if you like how that looks. On one of the versions I made, I liked that look and kept it that way. (It's Selma's sweater--the child's blue one.)