Powershell Command

Question

The current licensing history is m365 E5 for the entire organization and for shared mailbox have M365 E5 eDiscovery and audit add-on license .

1) apart from the default audit actions that are available we have enabled additional audit actions that are not within the default set of audit actions: We want to know

a. Is there any performance impact on the mailbox?

i. Example:

1. Slower retrieval of emails from the server?
2. Slower sending/receiving of emails?
3. Slowdown in search response?

b. Is there a way via powershell to test/validate the performance of a mailbox, in regards to above configuration change on enabling additional audit actions?

2) We had subscribed to M365 E5 licenses for all our users and shared mailboxes have M365 E5 eDiscovery and audit add-on license, this have effectively enable advance auditing for all our mailboxes and Microsoft documentation state that default audit data retention policy is 1 year for advance auditing, ref: Manage audit log retention policies - Microsoft 365 Compliance | Microsoft Learn  

a. How can we validate that default audit data retention policy is successfully applied on all mailboxes ? (Possible question during external audit)

i. Example:

1. PowerShell commands
2. Setting information in the respective portal

Please help with detailed information and link along with PowerShell commands