tax consequences for joined owner

I am planning to sponsor my son to purchase an apartment in NYC. We will be joined owner of this property. He will get a loan under his name alone (I am not co-borrower). I will contribute towards down payment. We file separate tax returns every year. I have the following questions:
1 Can he claim property tax on his tax return without splitting with me?
2 When we sell this house in the future, do we need to split real estate gain/loss? Or one person can claim all?
3 Is gift tax involved anytime at purchase or selling of the house?