well, before you start modding, you need to have the end goal in mind
for example, EVERY upgrade part has a tradeoff... your factory parts are the best mix of both.... that's why they're there.
you have to know if you're looking to gain high end hp at the expense of driveability and torque, or if you want torque, at the expense of high end hp....
and secondly, you need hp goals..
for instance, if you want to go 200+hp, you're not gonna get there naturally aspirated, which would rule out buying a header or an intake or software now, because you're gonna need to replace them anyways...
in fact, if you were gonna do a turbo or a supercharger at some point, there's not a whole lot you can do that wont need to be replaced, and used car parts are worth right around 0% of what they are new.....
Not trying to intimidate you, but if you don't have some goals in mind, you're gonna waste a lot of time, and money.
And chances are, if you do nitrous on a stock engine, there wont be much left to turbocharge, if that's one of your goals.
you could possibly choose what range of engine speed you're ultimately going to try and max out, and get yourself a cam, or a customized intake manifold (not an "intake" an actual manifold, short runner for high end, long tube runners for low end, etc.) those would be my two picks if you're serious about going turbo later on.
Either that, or suspension, breaks, a differential.... All things you can do now, and wont need to be changed again once you go turbo, so long as you buy good enough parts to perform correctly with your ultimate hp goals.... Remember, 300hp's worthless if you can't turn, stop, or get the power to the ground (unless you're gonna drop big $ just to do donuts like some retards do) lightweight wheels and nice rubbers are an ok upgrade, but are likely gonna need replaced by the time you're ready to step up to the big leagues..