amazon online backup

The application im looking to have developed is an online backup application. Effectively its backup application which checks for changed or new files then on a schedule sends them up to a server (in this case Amazon S3 storage) when a file has been backed up it will get a new 'icon' similar to the way that a shortcut gets a arrow icon, the same for files which have not been backed up. We would be looking to get both a client side application built (initial win only, with a view to a mac version later). files would be need to be encrypted before being sent and de duplication will also need to be performed (this can be client side or server side (although client side perfered) The application would 'talk' to a web service to get information about the amount that could be backed up (there will be a limit per gb) and messages which should be displayed to a user (such as you are near capacity if they are at 90% of their allocated storage). there will also be a restore function which will allow the user restore and also 'browse' backed up files. A small part of the application will provider for user managment to allow for the allocation of storage amounts to be allocated to users and also billing amounts. examples of both client side and server side applcations will need to be provided as example