Generally, when you start to shape a neck edge the way you're thinking of doing it, you knit across your first section. Then attach a new ball of yarn and bind off those center stitches, and continue with it to knit to the end of your second section. This way you have a separate strand of yarn for each side in place. You can work both sides at once this way, using a separate strand for each--helps make sure you decrease at the same rate and on the correct side.
I find that k2tog is perfectly adequate for the decrease and for picking up the stitches later. the slant won't matter since it'll be behind the edging, and k2tog makes it nice and tight.