1 - I'd say yes. The Sport package is worth it. Both for you, and for resale value down the road.
2 - If the new Nismo is any indication, we'll probably be waiting until 2016 at the earliest for a major re-design or new version. As for just a new 2015 model, I imagine we will see those later this year - whatever they may be.
3 - White is sexy. Black is also sexy. I prefer white, but I would argue that a well kept and clean black car is hard to beat. Keeping it clean though, be prepared to put in a bit more effort than with other colors. If this is a car you're planning on keeping for a while, I'd say to broaden your search or wait for the 2015s to get the color you want. When you're investing this much in a car, you don't want to 'settle' for a color you didn't really want. You'll regret it for years.
4 - Read this helpful thread. I learned quite a bit of helpful stuff from it.
New Car Buying 101. Please Read Before Buying Your Nissan 370Z