I just want to understand what is going on when installing KDE.
What is the difference between plasma and plasma-meta?
So what is this qt5ct application? And why do I have to modify the nano /etc/environment file and comment out this line QT_QPA_PLATFORMTHEME=qt5ct? What does this do?
Lastly what does the discover tool do?
https://wiki.archlinux.org/index.php/KDE#Plasma
https://wiki.archlinux.org/index.php/Meta_package_and_package_group
That qt5ct thing , if you use a gtk based desktop is to setup qt theming, for qt applications is not needed for qt based desktops. Plasma-meta is a empty meta package with all of arch recommended packages as depency, plasma is a group to then you install a group of packagee diffete’t packagez belong 'to different groups
So Xfce is a gtk based desktop and KDE is a qt based desktop if I am understanding you correctly?
I see, so which one would you personally recommend me to install then?
I usually install using the plasma group without a couple items (like Discover) and add a few extras like Dolphin, Konsole, Gwenview, Ark, and Ddialog. You can exclude packages by using ^ before the number listed for that package.
meta files vs groups, with groups you can remove some individual files with a meta packages is a bit different… it cant remove individual packages… its not dat you need all in the group basicly
Thanks for explaining that 
I just want to understand this last bit, so qt5ct is the package that controls qt applications/desktop environment, am I correct? And this is for XFCE, right? So I have to remove it because KDE uses somehting different?
And what is the discovery tool?
Qt5ct you set qt theming for the gtk based. To choose gtk2 it will set qt to theming its a hole. Kde is qt so qt5ct is not needed.
Discivery is like the kde version of software. If you do pacman -Qi discover and add optional deps you can use it as software store but if you dont take tje optional you install things like sddm theme other kde stuf but i believe install such things already integrated in kde