Here are my first mods (in order):
Tints
Xenon White License Plate Lights
BC Racing Coil Overs
OEM Sports Wing
Rear Diffuser
Japanese 370z Plates
Dipped OEM wheels
Wider Rims and Tires (9.5 F and 11 R) wrapped in 255s and 285s
Fast Intentions CBE (on order)

Planned for this Summer:
Stillen Gen 3 CAIs
Double Din Head Unit & Sub

Winter Project:
Amuse Body Kit

2 Year Goal:
Twin Turbos
Work Meiser MR1 Wheels

By the way, where do I get a forum sticker?

Tinted windows, lowering springs, tire graphics, and now deciding on exhaust? I think I will go with motordyne CBE but I want FI test pipes. Does anybody know if the bolt up together? Then stillen CAI

RJM Performance Adjustable Friction Point Clutch Pedal Assembly

This should be everyone's first mod if you want to love your Z more. The dealership employee told me I would get used to the clutch..... I didn't after 1,000 miles. Ryan at RJM fixed that for me. In fact, now that I am going FI, I ordered RJM's new HD Master cylinder and the newest revision of his pedal because I love that company so much.

Ive owned my 2016 Base 6 SP for 1 year now.

1st - WeatherTech floor mats
2and - FI Start button
3rd - Nismo Carbon Gear shift knob
4th - Stillen CIA - immediate and noticeable performance gain.
5th - FI CatBack - just installed yesterday. A little louder than I expected (with 18" resonators). I have not had a chance to drive it much, maybe 10 miles and so far its all been under 50MpH so can't say too much about it, however I do feel there is some extra power there, not sure 'how much.' It does sound cool, louder than expected, but cool.

Next upgrade will either be the pulley or HFC. Not sure which will come first. Pulley sounds easy and inexpensive for a extra 5 HP.

After that its a toss up between coilovers or stereo. Since my home stereo is a $20,000 setup, I don't value car audio all that much.

Oh my god that is sexy. How would you rate the difficulty of installing air on the 370z on a 0-10 scale? Just this month I've helped two friends bag-over-coils on their Mazdaspeed 6's and it's a pain the *** with some welding required.

Thanks to this thread I just ordered weathertech floor mats.. lol

I haven't read entire thread,,,but as far as Horsepower to the the Wheel's;bolt on's from front/back will get you (50-75)...pending on how much $$$$ you put to it.
A good Twin Turbo set-up (250-300+)...a huge difference & still on pump gas-just more $$$$$.
Keep looking through the thread's & spend wisely.....as it doesn't take long to spend a small fortune...(or large one 25k & up)

The previous owner of my Z upgraded:
-Head unit (its mostly for iphone) but i bluetooth and am happy.
-K&N intake so I can't complain.
-Weathertech floor mats.

I have '14 nismo so the exhaust is pretty good. Don't think I need to change that for a while. (when I save enough for F.I.)
I am adding a 4th brake light which I just purchased.
Then tinting windows.
Getting better all-season tires. I am a fan of Continental.
Then maybe upgrade front speakers.

I think you will have a great start with the replies in this thread.

My favorite Mod was the Nismo Wheels and spacers. I stilll get that feeling like when you see a good looking girl in jeans and a sweatshirt and then you see her in a dress and heels.

Just completed my first "mods". 15% tint all around and clear bra. Not going to even think about power mods until I take this baby over 4k RPM....damn you break in period.

Weighted shift knob and some fat wheels / tires. And Stickers

1st mod

lowering springs. This car needs to be dropped lower than stock. Changes its look drastically. No more monster trucking.

Yeah, but it takes more than just springs to lower the car. You need camber arms and toe bolts unless your second mod is a new set of tires.

The modification I would do first would be a 24 or 34 oil cooler holy old thread Batman and I know the370z.com decals are worth at least 20 whp.

1st Mods To My New 370Z
 

The first mods I applied to my new Brilliant Silver 370Z was to "De-Hamburger" it and add a front pewter plate for my military alma mater...

https://goo.gl/7BboZZ

... the pewter plate is quite striking with the brilliant silver paint scheme.

1st mod were catbacks to make it sound as sexy as it looks :rofl2:
2nd mod were intakes along with the catbacks gave me a little more HP
3rd mod STANCE coilovers
4th mod were wheels and rims from 18" stock to 19" powder coated rays with off set Hankook's 245/40ZR19 in the front and 275/40zr19 in the back with spacers
5th mod front lip/side skirt diffusers
6th Seibon GTR inspired carbon fiber hood
7th TINT -done for now and really glad i went with a stock 370z so I could do all this.