Andrea Bocelli has such beautiful voice and heart. The Prayer he song with Celine Dion is my favorite.
I haven't heard many of his songs but know he sings Opera right?
He may sing Opera. But he is on tour a lot and has had many concerts.
I think the only song I've ever heard him sing is Time to Say Goodbye.
Time to Say Goodbye is one of the songs he has song many times. 
I think maybe I have heard it at a wedding. Is that common?
That sounds very interesting to sing Time to Say Goodbye at a wedding. But if the new couple like it, that is a very beautiful song. You should listen to The Prayer. 
You said that's the one with Celine Dion on it correct?
Yes. Celine Dion once said that if God has a voice, it must be quite like Andrea's. 
That is a fantastic quote.
It's amazing that he has been blind since infancy, but sings so beautifully. His songs really comfort people's hearts.