It doesn't matter all that much what you use since you'll be seaming, but some people like to ssk on the right edge for a left-leaning decrease and k2tog on the left edge for a right-leaning decrease.
And yes, you'll be doing one at each edge.
"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