Measurements and increases.
So I emailed Shelley Mackie and she wrote back to say that:
center back should measure 21 1/2'' between armholes
entire sweater laid out 43''
edging 1 1/2'' (making the sweater 41 1/2'' to the edging and then 43 with it)
Am I really confusing you? Shelley also commented on my post entitled "Measurements Anyone?," if you would like to see her response (this is kind of my translation).
I decided to do 31 stitches between yos. I think that that should work well for me. If anyone has trouble with the provisional cast-on, I found www.knittingatknoon.com/provisional.html extremely helpful. They have a video that was great. Go pinwheelers, go!