sudo pacman -S mate and select all
To customize go to gnome-look.org and most GTK2 and GTK3 themes will work.
Go to System> Preferences>Look and Feel>Appearance and you can install the themes there. (Some themes will come with a built in installer)
To install Icons just download them and extract to /home/user/.icons/ (your user only) or /usr/share/icons/ (must be extract as root, installs icons for all users)
To change the icons just edit the theme in the appearance program.
Hope this helped