Licensing advise for BE20.1

I'm looking for some advice on the best licensing options for BE20.1.  I'll need to back up a server running backup exec as well as 2 additional windows servers that both have Active Directory on them.  I prefer perpetual licenses to the capacity or term license options but am not sure exactly which licenses I'd need...there's mention of agents for Applications and Databases which would be required (I think but am not sure) in order to fully backup AD properly.  Also, from what I understand, the OS on the Backup Exec server should be the same as the OS on the domain controllers running AD in order for the AD backups to fully backup with GRT, correct?  I'm going to be backing up Server 2012 R2 domain controllers, which would mean the BE software must also be on a Server 2012 R2 system?  Basically I'm trying to figure out exactly what I need...based on what I've read I think I need

1 BE Server License perpetual license plus 2 agents for Windows along with 2 agents for Applications and Databases (1 agent each for Windows and Apps/DB per AD server?).  If someone can please advise if this is correct or if there are other licenses/qty needed.  Thank you