If you want an Alfine hub, then you are far better off financially buying a bike that is equipped with one. Upgrading something as significant as the drive train is usually quite silly on a new bike. Tires, saddle, grips and pedals might make sense, but anything else says "buy a different bike" to me.

To change to an Alfine (if possible) would mean a new rear wheel and shifter, which you would have to buy at retail. You would also be left with a rear wheel, derailleurs and shifters from this bike, which you could sell, but at used prices. And used prices for that level of component are pretty low. In addition, you would need to replace the crank and/or do whatever you wished in order to only use a single chain ring.