Nice work; I also love the postcard effect. I like the different edits, especially the one by Chris. Tom's is great too, but as he says, he takes it in the direction of photography and I prefer the old-fashioned Norman Rockwell effect. Your choice of course. I do think you made the overall image too dark in your second version. I think the details were better when it was lighter. Somewhere in the middle would work for my tastes.
As to why you need multiple light sources, it's because there are multiple light sources. The one you first use is from the street lamp to the left of the boy. There is also the moon which you show as very full and very bright, so it too would cast a shadow. Maybe that shadow would not be as deep as you made it. I'd be interested in other opinions on that.
Anyway, it's a super concept and a good composition. If you wouldn't mind, we like to see the collection of source pictures you used. Hey, we can ooh and ah even more when we see the adjustments, selections, positioning, and so forth; all the work you did to put it together.