"This'll be my first go at 3 needle bind off as well, so I'll have to get some dpns (which I have been putting off)."
You're getting the dpns just for the 3 needle bind off? You don't need them (unless you'd like some for other reasons). You can slip the sts from the back shoulder onto any smaller size needle and then use one end of circular fot the front shoulder. Use the other end of the circular to knit the bind off. I'm assuming the circular is the needle you've used to knit fronts and back and it's the only one that matters for the gauge of the bind off. You'll love 3-needle bind off- so sturdy and neat looking.