Franco,
I don't have an answer related to OwnCloud, however have you looked into the Microsoft Office 365 for Education? Qualifying educational institutions receive the essential subscription for teacher and students for free (web apps, 50GB mailbox, and 1TB OneDrive). That, combined with the Office 365 integration for Moodle should meet your needs, especially if you use the Office 365 authentication method for Moodle.
~ Bryce