Scalibility issues in CMS application?

Hi All,
      I am creating on CMS application and there i am providing feature
to create document.
I have some issue about scalibilty in CMS:

1. How to make size limitation when user is going to create document.

2. How to make size limitation when user is uploading some documents.

3. How many documents can we create in CMS their is any limit??

4. How to handle database scalability for CMS application.

Please reply if you have some clarification about any point.

Looking for your help.

Thanks & Regards,
Varun Kumar