If you don't understand, then you didn't get the movie or the character.

As Kris himself says, lately he's been worried about our attitude toward Christmas. It seems we're all so concerned with making things go faster, fly higher, etc., that Christmas and he are getting lost in the shuffle. But as he finds out (and as we know), the meaning of Christmas may be beleaguered, but it isn't lost at all.

Because Kris wanted to observe humanity's general opinion of him. New York City was ideal for this because he'd be able to find every imaginable type of person. As far as I'm concerned, even in the 1940s, NYC was one of the most sought out cities on the planet.
Kris surely prepared sufficiently to "run the show" remotely from where he lived, first in Great Neck and then NYC. Otherwise, he must have had a 2nd In Command take over.

He was there to see the Rockettes Christmas show at Radio City Music Hall.

Well in 1947 the allies had just defeated Hitler (1945) and New York represented the "state of modern man" since most of the industrial trading nations were trying to rebuild the very infrastructure of their countries from the aftermath. New York also represented modern man's cynicism so Santa had to jumpstart his agenda and give people something to believe in right there in the Big Apple.

He had elves running things till it was time to deliver all the gifts

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Didn't you watch the movie? Of course he was real!
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The main reason that Santa is so jolly is because he knows where all the bad girls live

You know that guy wasn't real right?

He delegates authority.
He's taking the knife out of the Cheese!
Do you think he wants some cheese?