Like others said... you can buy aftermarket or find used sport rims. Is it cool? Forget what we think is cool. Its your future car... whatever is cool for you is cool. The only person you need to imprress is yourself. Its your purchase and no one will be paying your bills but you.
If I were you i'd look into your price range for a Z vs the sport pkg and compare to eventually going aftermarket wheels. Base wheels aren't the hottest thing going but aren't hideous. I know I would eventually want to replace them if I had them.
So in other words, my best advice is do what's most affordable and logical for your situation. You can buy the sport pkg. In my opinion, its really cost effective because what you will pay in good tires and rims... will cost as the same as the complete sport pkg. BUT. What's your appearance vision for the Z? Do you think aftermarket wheels will make it feel more personal to you? Maybe in one color the sport pkg is hot and in another aftermarkets would do more justice? Functionality... does the sport pkg have more of what you need and you just don't know yet??? Some things to consider...
Sport pkg functionality.
For street driving, or even AGGRESSIVE street driving, its more than you really need.
For the track. Its good but needs some mods. Brake fluid upgrade, I personally think steel lines are great on a safety level. Stillens brake cooling kit is also a must. And for more even wear, id add rotors to the mix. So you would be looking at about $1300 to upgrade the sport pkg brakes to a full track braking system.
On base brakes for spirited driving, EBC 3GD's and yellow stuff pads will give you a highly aggressive BBK like feel for half the price... lines would be much less necessary considering that your braking would be less extreme.
Base tires are much cheaper than the 19's and give a more street compliiant ride. Replacement tires like continental DWS will increase performance greatly from the stockers and still provide a more compliant ride.
Or you can just leave all of that stock and just have fun. Just remember, on stock brakes. The Z is hard to cause fade, but will fade if you are persisently aggressive. Also, nissan has a nice wheel option for 370's for 1650. They aren't bad looking and have a light chromey polished look if that's your taste??? Go on nissanusa.com under accessories and see if you like them. I think in certain colors they are nice.
I'm giving you some extra info because its common to drive a sports car for a while and eventually want to make improvements. You may decide to take a crack at the track. The Z is one of the most fun cars out there and you may get "the fever"?
Just think it through, don't rush and most importantly. Do what makes you happy. Hope to have you in the Z family soon.
PS. If you go for an aggressive Z? Oil cooler is Necessary.
Disclaimer: this is my personal opinion based on some experience with my Z and other info has been learned through the forum and reading articles. This is a base guideline that can be used as basic advice. I do not endorse any brands mentioned. They are examples of your possibilities.