I would stick to the venders on this forum (go to marketplace). I ordered a bumper from Arch industries and received it a week after ordering/paying. Keep in mind that's counting shipping from Cali to Alabama. I plan on posting a review once I get it painted. I already installed it, but they didn't send the mesh (they had a shortage) so once I get it, paint time.

Looks: Completely up to personal opinion. I don't like the 2 vent style of the OEM bumper, and like the layout of the k2. Wheels, etc. All just personal opinion. It's your car, do it how you would love it more.

Handling: This goes for pretty much any car. Wider, stickier tires. After that, get the suspension up to par with sway bars and stiffer springs/shocks (coilover is the way to go).

Power: Z tube, revup air box, k&n filter, test pipes, cat back, and a good tune (Osiris, in my opinion) and you can get another 25-45ish hp depending on how good of condition your motor is in.

Simple power: Vortech. Dont have to build the engine and you can make up to around 350whp.

Bigger power: Single turbo. Don't have to build (up to about 400whp safely without for 5AT) then if you build the motor about 550 whp will be the limit. Basically.

Huge possibilities for power: Twin turbo. People are making up to 1000whp. Building isnt a must, but highly suggested for anything over 450whp. But at that point the 5AT (even with some mods) will have issues.

But its not even remotely that simple when you get into Forced Induction. If you're interested in that, check out the my350z FI forum.

Here http://my350z.com/forum/forced-induction-182/