I would probably do a knitted or cable cast on at the ends of the rows in question. Amy has video of both in the Basic Techniques section.
So work across, add six, turn and work across, add six.
Work across add 18, etc.
As for the yarn, your sweater will just turn out bigger than the original.
"Trust the pattern!"
Time flies like an arrow, but fruit flies like a banana.
Hop aboard while we follow the cloud-covered van of knitting harmony, man!! Woooo!! --Hedgehog
IngridKH on Ravelry