I think we'll have two or three.....as I'm no longer a spring chicken but a summer chicken and getting a little long in the tooth I'm taking the wait and see how we go approach. We have one and are currently trying for another. If I was younger I'd say 3 most definitely.
I'd also agree that I like the idea of a child having siblings so they have someone there in times of loss (like when us parents fall off the perch).