Installing Backup software should be enough for the kind of setup you have. Also, check what you are licensed for. Infrastructure manager is a separate software which can be used for managing updates for Backup Exec, but it would require a lot of resources on the server. As this is a domain controller, i would not recommend loading the infrastructure manager on this server. So, i would suggest going ahead with backup Exec software only on this machine and rmeote agents on your workstations. That should be enough for you to perform backups of your workstations.
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