Activity logs are kept for 90 days. You can query for any range of dates, as long as the starting date isn't more than 90 days in the past.
Through activity logs, you can determine:
* what operations were taken on the resources in your subscription
* who started the operation
* when the operation occurred
* the status of the operation
* the values of other properties that might help you research the operation Reference:
https://docs.microsoft.com/en-us/azure/azure-resource-manager/management/view-activity-logs
https://docs.microsoft.com/en-us/azure/automation/change-tracking

Firewall policies work across regions and subscriptions.
Place all your global configurations in the parent policy.
Note: Policies can be created in a hierarchy. You can create a parent/global policy that will contain configurations and rules that will apply to all/a number of firewall instances. Then you create a child policy that inherits from the parent; note that rules changes in the parent instantly appear in the child. The child is associated with a firewall and applies configurations/rules from the parent policy and the child policy instantly to the firewall.
Reference:
https://aidanfinn.com/?p=22006