Microsoft Word - Backup Exec 21.1 Licensing Guide Sep20.docx (veritas.com)
for Q1 and Q2, i think you need to have same version of both products to work properly.
For Q3,
Agents and Features Custom Edition
Licensed per Details
Backup Exec Server Backup Exec Server
Included in Bronze,
Silver and Gold
The Backup Exec Server manages the backup environment
(agents/options) and all tape/disk/cloud storage devices
used for backup and recovery. Each Backup Exec
environment requires at least one Backup Exec Server.
Custom edition licensing: each Backup Exec Server license
includes 1 Agent for Windows to protect the local Backup
Exec Server.