WM

Display server

pacman -S xorg 

Display manager

pacman -S 
  lightdm
  lightdm-gtk-greeter 
  lightdm-gtk-greeter-settings 
  # xorg-xinit

sudo systemctl enable lightdm
# sudo systemctl enable sddm - Plasma

WM - I3

pacman -S
  i3-gaps
  dmenu
  thunar
  nano

WM - XMONAD

pacman -S
  xmonad
  xmonad-contrib-git
  xterm

DE - Plasma

pacman -S
  plasma-meta
  kde-applications

DE - Plasma + I3

Write the following into /usr/share/xsessions/plasma-i3.desktop

[Desktop Entry]
Type=XSession
Exec=env KDEWM=/usr/bin/i3 /usr/bin/startplasma-x11
DesktopNames=KDE
Name=Plasma with i3
Comment=Plasma with i3