The 8-ply would be the place to start as it's closest to the recommended yarn for the pattern.
But the number of stitches per inch(cm) is going to vary anyway just because knitters are different and their tension is different. You might need a smaller needle to get that yarn to the correct tension, or you might not if you're a tighter knitter. (I'm fairly loose, always have to go down needle size or two to get gauge.) You really won't know precisely until you have it in front of you and on the needles.