At least one: the antenna from the ESP is perfectly shielded. Check the 
design guides for an ESP PCB design.

Stephan B. wrote:
> Any help is gratefully appreciated.
Usually it first time operation doesn't work the way "switch the power 
on and all runs ok". Instead you must do it stepwise:

1. apply supply voltage
2. measure the supply voltages on the devices supply pins
3. bridge rx and tx at the CH340 and check it with a terminal programm
4. ....
5. ..

> Any help is gratefully appreciated.
The pins in good readable schematic symbols are not sorted in the 
package order. Instead they represent the function of the device: inputs 
right, outputs left, supply top and bottom.
Simply have a look at other good readable schematics. Compared to them 
yours looks a little bit like the scribbling of an kindergarten child.

J. S. wrote:
> the antenna from the ESP is perfectly shielded.
First thing is to read the data sheet and second is to have a close look 
on other boards.

Thank you, for your recommendations. Currently I am not having an error 
connecting to it wirelessly, I habe trouble uploading a sketch, I get 
the feedback that it failed to establish a connection. Also, when it 
tries to connect, the builtin LED blinks for 10ms or so and then goes 
dark for another 2s.

And yes, I know the design isn't really good, since it is my first ever 
ESP32 custom PCB _:)
I am just trying to get this to work, so I can install WLED to it, then 
I can improve my design and do a 2. Rev

You need a 100µF capacitor near to VCC/GND pins of the ESP12 module.

GPIO15 needs a pull-down resistor.

U3 must be connected to GPI0, not GPIO10.

The pin row on the short side (opposite of the antenna) must NOT be 
connected, because they are used for the flash memory.

See http://stefanfrings.de/esp8266/index.html

Notice the "translate" link in the upper right corner.

Thank you very much for providing that Link, it helped me a lot! I was 
copying the D1 mini schematic, but it seems like, I have made some 
mistakes...
I have now corrected it according to your instructions. (Find the photo 
in the attachment)
Are there any other flaws?

Stephan B. wrote:
> Are there any other flaws?

I noticed that you used GIO02 twice (for the LED1 and the red output). 
But that might be on purpose.

Yes that is on purpose. To that board you can connect a 5V ARGB as well 
as up to a 24V RGBW LED Strip (not at the same time of course).