Explanation
https://blog.pragmaticworks.com/what-is-azure-advisor#:~:text=Microsoft%20defines%20Azure%20Advisor%2

Explanation
The VNet will be marked as 'Non-compliant' when the policy is assigned. However, it will not be deleted and will continue to function normally.
Azure Policy is a service in Azure that you use to create, assign, and manage policies. These policies enforce different rules and effects over your resources, so those resources stay compliant with your corporate standards and service level agreements.
If there are any existing resources that aren't compliant with a new policy assignment, they appear under Non-compliant resources.
References:
https://docs.microsoft.com/en-us/azure/governance/policy/overview
https://docs.microsoft.com/en-us/azure/governance/policy/assign-policy-portal

Explanation

Box 1: Yes
Most services go to private preview then public preview before being released to general availability.
The private preview is only available to certain Azure customers for evaluation purposes. The public preview is available to all Azure customers.
Box 2: No
Azure services in public preview can be managed using the regular management tools: Azure Portal, Azure CLI and PowerShell.
Box 3: No
Services in private or public preview are usually offered at reduced costs. However, the costs increase, not decrease when the services are released to general availability.