You can bind off on the purl row, which one really doesn't matter, as long as it's at the beginning of the row.
As for the decreasing, yes, you're plan is correct.
"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