Yes, you can use the content of your multiple websites in the Contents application in different setups.
Yes, you can create your content within the Intranet and publish it only for your staff.
Yes, you can turn comments on and off on the content you want.
Yes, you can back up all your content and documents in it by using your Import / Export feature from the transfer wizard.
You can also take the entire Entranet backup using the Control Panel applet.