l have 2000$ to spend on my 2007 350z 3.5l V6. what are the best things to buy that will combined add the most HP/torque to the car

Save about 2K more and add a Stillen supercharger :)
If you are impatient, you can get a Skunk2 intake spacer, cams, ECU flash and a ca-back

Headers high flow cat converters exhaust system by Stillen and Dynometer tuning. Cold air intake system. That will be good for almost 289 at the wheels.

ecu retune uprev.com they do nissan only great hp/tq gains

Nitrous wet system kit 80shot, re flash ecu, cold air intake, cat back exhaust, fuel pump w/regulator, and a car freshener.

l have a 2004 350z with Vortech Supercharger, Kinetix Intake Manifold, Resonated test pipes, headers, & hks exhaust for my power mods. l would highly suggest the Resonated test pipes by Labree or Invidia, any headers will do, & exhaust. The intake manifold is just for show. If would rather stick with the plenum spacer. l felt a good amount of power with the resonated test pipes (Labree), DC sport headers, & HKS exhaust. Check intensepower.com or hopupracing.com. Hope this helped! Enjoy the Z!

If you want the absolute most power I'd save money for turbo or supercharger. Intake, exhaust, and other bolt ons are pretty good too.

google it!!!!!

Exhaust System
Cold Air Intake or Short Ram Intake.
Under drive pulley

That should use up your $2,000.