The problems

After installing lightweight window managers, I noticed that some gtk applications didn't work ( thunar or nautilus, for example ) because of a dbus problem. Moreover, the gtk applications looked ugly, the icons didn't show up.

making dbus run

You have to add the following line to /etc/rc.conf

dbus=YES

Don't forget to put the right dbus file in /etc/rc.d

cp /usr/pkg/share/examples/rc.d/dbus /etc/rc.d/dbus

choosing your gtk theme

For gtk2+ applications, you need to create a .gtkrc-2.0 file in your home directory with the following lines :

gtk-theme-name = "Clearlooks"
gtk-icon-theme-name = "gnome"
gtk-font-name = "Sans 12"

For gtk3+, the file is ~/.config/gtk-3.0/settings.ini:

[Settings]
gtk-theme-name = Material-compact
gtk-icon-theme-name = adwaita
gtk-font-name = Sans 12
gtk-enable-animations = false
gtk-application-prefer-dark-theme = false
gtk-menu-popup-delay = 0