I leak occasionally and maybe only a few teaspoons at a time, and that sometimes when naked (like in the shower) or braless (in bed). I have eight pads but have never used more than four before the baby's clothes needed washing. I confess that often I don't wear them, because I just don't care that deeply if my hanging-out clothes get milk spots on them, and the leaking isn't as bothersome as the pads are lumpy. Sometimes if I think the non-occupied breast will leak while I'm nursing, I temporarily tuck the burp cloth in my bra. I have occasionally used breast shells when having a sore nipple, and have found those more useful (they also collect leaks, though that isn't their intended purpose).
Based on my experience, I would say get just 4 (2 sets) and then see how it goes when you've had your baby. You may find you don't use them much, and if you do you can get more and use baby socks or baby washrags or flannel wipes as a (lumpy) stopgap!