I think most people decide on how many to have based on their own childhood experiences. I was an only child and hated it so i was desperate to have more than one. A lady i spoke to at my dh's previous work was the last of 3 and she so hated all the fighting and bullying that happened to her that she was dead set on only having one, so i guess it all depends on your own experiences and how you feel. it's no one elses business really and you certainly shouldn't be judged on which decision you come to.
When i listen to my boys giggling togther and catching them cuddling i know i made the right decision for me as that is exactly what i missed. (they do fight a bit too though so you can't always win!)
emotive subject for most and only you can know whats right for you.

enjoy your bub

Julie x