Yes, when users are created, they can be associated to one or multiple sites.
Customers can have their own custom roles with particular sets of permissions to control which group of users can perform what tasks within the system. This applies to both internal and external roles.
C3 constantly monitors its systems and will use all reasonable efforts to promptly react to any type of incident. C3 has a Business Continuity Plan in place for the Hosting and Processing Environments and has established a detailed Disaster Recovery Plan. SQL servers are in mirroring and we have monitoring tools with alarms to ensure all the data backups are running properly.
C3 guarantees between 99.0 % and 99.9% uptime depending on the selected Service Program package.