You can change the time of inactivity after which to turn the screen off from terminal using next commands:
gsettings set org.gnome.settings-daemon.plugins.power sleep-display-ac <nr_of_sec>
gsettings set org.gnome.settings-daemon.plugins.power sleep-display-battery <nr_of_sec>
gsettings set org.gnome.desktop.session idle-delay <nr_of_sec>
Change <nr_of_sec> as you wish. For example, for 3 minutes, use 3x60=180:
gsettings set org.gnome.settings-daemon.plugins.power sleep-display-ac 180
gsettings set org.gnome.settings-daemon.plugins.power sleep-display-battery 180
gsettings set org.gnome.desktop.session idle-delay 180
If you will use 0, the screen will never turn off.
Source: https://askubuntu.com/a/313155/147044.
To change the brightness through terminal, use this answer: https://askubuntu.com/a/56171/147044. I tested this method on 13.04 and is working.