Wanting to build a server to run OXApps but needing to know storage size

We're planning on using external Mailstore & filestores so space is not there an issue in regards to mail and documents.

Planning is based on http://oxpedia.org/wiki/index.php?ti...X_Tutorial_10K

If mail & files are stored on external servers - how much storage space should we allocate to the OXApp server itself and the rest of the components?

We will be running at minimum
OX AppSuite Pro
OX Drive
OX Documents
OX Guard
OX Webmail
OX Sync

Documentation states minimum space required is 500M + user data. I'm guessing most of this data is stored in the db and would be rather small in comparison - would rather not under provision though

Does anyone have any suggestions/recommendations?