Usage at your own risk. Be ready to do your own research if you run into any issues that are not mentioned below!
Since I did not want to keep the original OS running on this particular MacBook, I wiped the hard drive in recovery mode. To get there, shut down the MacBook completely. Then, power it on again and press:
cmd + r
The apple symbol should appear and you can wipe the hard drive or create another partition for your Kali installation, if you choose to keep MacOS as a second operating system.
At the same time, but on another computer (Windows), i prepared the bootable USB stick with Kali on it:
I put the Kali .iso file (link below) on an USB stick with the Windows tool "Rufus" (link below as well).
To start the installation process, we need to boot from USB. Shut down the MacBook completely, then power it on and keep the following button pressed:
You should now be able to select the USB stick to boot from and follow the guided installation process.
My issues during the installation:
It would ask for the file b43-open/ucode29_mimo.fw, which means Kali does not have the correct driver for my ethernet card out of the box. That's okay, we can install it later and will skip this part of the installation for it now. Once the process is finished and Kali is up and running, connect the MacBook to the internet via cable. Then run:
sudo apt-get update sudo apt upgrade -y sudo apt install firmware-b43-installer
Now, just restart the MacBook and WiFi should work now!