Yeah I have done that before with JLCPCB, but only tht componets soldered by myself.
But I have the advantage that my company is the leading producer of Reflow soldering ovens so the LEDs should be no Problem
There you go. So it'll be a little quality test run of your ovens in other words 
Well, I'll do another test run of the ol' bed here
- Is this for a miniature or full size area ?
Area?
-
How long will the LED string be, how high from floor ?
-
WS2812b LED strings are quite bright at 6 feet.
I Cant use a traditional Strip.
It will be on the ground, not lighting up a surface, it just needs to be visible as best as possible without blinding traffic.
20m Long with 40 LEDs so 2LEDs per Meter
As a sort of guidance for drivers where to go
Google (actually Bing, which Is Not Google), shows Adafruit has addressable LEDs in high wattages: Ultra Bright 4 Watt Chainable RGBW NeoPixel LED - Cool White [~6000K] : ID 5162 : Adafruit Industries, Unique & fun DIY electronics and kits
*Please note: these are high power LEDs, you need a strong 5V power supply that can provide at least 1/2 A per LED
Is in the discription of the LEDs
Wich means i put my Powersupply on the Vcc, with my data line coming from the arduino
and my Ground being common between the two
What LEDs do you have?
these ones
QLSP04PCAU
I found them, I didn't read the entire thread before. My mistake
Hi, @moax8898
Welcome to the forum.
What exactly is your application?
What does your project do?
Thanks... Tom.... 
50 x 350 mA = 17,5 A
At 5 V you're gonna need some thick wires. Where will you inject? At one end, two ends or the middle), both ends and middle?
One more thing, is there a possibility that people will walk over the installation, or tires run over?
ideally i would inject only on one end.
You think 1,5mm² would be enough or should i use 2,5mm²?
Tires and feet could happen but really only in a worst case scenario, so shouldnt be a problem
actually now that i think about it the middle would also be a possibility, so 10m in each direction
No. To both mm². You will get voltage drop, especially if you power the strip from one end only. Ideally, you would use a higher voltage, with PWM. (That's why the MOSFETs are there for anyway).
Lets see if there's a calculator out there.
Not to sure why you would want to use an LED driver to control a MOSFET switch but you do need to use all 3 outputs AND they must be pulled-up to 5V.
The logic will be inverted.
You should also have a bypass cap on Vdd and series resistor in the data line.
So a MOSFET can be used to regulate Voltage?