Are there any reports or scripts that would generate reports letting you know the following:
When the last time the Archive was accessed
How often an archive is accessed
Which users have access to that archive.
The first two can be done at the Vault Store level (when and how often are items in a Vault Store accessed) by the Archived Items Access report. It requires that you enable Auditing in the environment to capture this access data.
I don't believe there is a report that presents this data per archive, but that information would be in the EnterpriseVaultAudit database if you wanted to roll your own SQL query.
For the third piece, there is not currently a convenient way to do this, but one should be coming soon. I need to state that this is no guarantee and new features are always subject to change, but if all goes according to plan, you should have PowerShell cmdlets to view and manage archive permissions in EV 12.4.