Two weeks is a LOT for NYC. I spent a week and it was plenty.
May I suggest catching a train to Washington DC for 2-3 days. It's not expensive and breaks up the time in NYC nicely.
Im sure, u'll get good tips on things do so I won't give u must
there. For cheap shopping (well, cheap is relative when you're staring at R15 to the dollar) take a tip to Woodbury Commons... It's a massive outlet mall. Buy the discount booklet for $10. You can add discounts in the USA unlike in SA. None of that nonsense about deals that can't be used in conjunction with any other offer, etc.
Most of all, soak in the city. The vibe is amazing!
Oh, one last thing, if u can, Google "The Ride" and take that bus tour on your first couple of days... It's good fun.