Using Identity-Aware Proxy (IAP) for managing SSH access to private VMs ensures secure access control and avoids the need for public IPs. IAP allows you to enforce identity-based access control policies.
Enable IAP: Ensure that IAP is enabled for your project. This can be done via the Google Cloud Console under "Security" -> "Identity-Aware Proxy".
Set Up Firewall Rule: Create a firewall rule to allow SSH traffic from the IAP IP ranges.
Navigate to "VPC network" -> "Firewall".
Create a new rule allowing ingress traffic on port 22 (SSH) from the IAP IP ranges.
Assign IAP-Secured Tunnel User Role: Grant the roles/iap.tunnelResourceAccessor role to the administrators who need SSH access.
Go to "IAM & Admin" -> "IAM".
Assign the IAP-Secured Tunnel User role to the relevant users or groups.
SSH Using IAP: Administrators can now use IAP to SSH into the instances. This can be done using the gcloud command:
gcloud compute ssh [INSTANCE_NAME] --tunnel-through-iap
Reference:
Using Identity-Aware Proxy for TCP forwarding
Google Cloud Firewall Rules

To ensure that PII data is separated from non-PII data, using Cloud Pub/Sub and Cloud Functions to trigger a scan by the Data Loss Prevention (DLP) API is an effective approach. This method allows for automated detection and handling of PII.
Steps:
Set Up Cloud Pub/Sub: Configure a Cloud Pub/Sub topic to receive notifications whenever a file is uploaded to the shared Cloud Storage bucket.
Deploy Cloud Functions: Create a Cloud Function that is triggered by the Pub/Sub topic. This function will invoke the DLP API to scan the uploaded file for PII.
Move Detected PII Files: If the scan detects PII, the Cloud Function will move the file to a secure Cloud Storage bucket accessible only by the administrator.
Set Permissions: Ensure that appropriate permissions are set on the Cloud Storage buckets to restrict access to files containing PII.
Reference:
Google Cloud: Data Loss Prevention
Cloud Functions documentation

"To support common use cases like setting a Time to Live (TTL) for objects, retaining noncurrent versions of objects, or "downgrading" storage classes of objects to help manage costs, Cloud Storage offers the Object Lifecycle Management feature. This page describes the feature as well as the options available when using it. To learn how to enable Object Lifecycle Management, and for examples of lifecycle policies, see Managing Lifecycles." https://cloud.google.com/storage/docs/lifecycle

Encrypt non-sensitive data with Google default encryption:
Google Cloud automatically encrypts data at rest using AES-256 by default. This minimizes key management complexity for non-sensitive data as it is handled entirely by Google.
No additional setup is required for default encryption, ensuring low latency access to the encrypted data.
Encrypt sensitive data with Cloud Key Management Service (Cloud KMS):
Cloud KMS allows you to create and manage cryptographic keys in a centralized cloud service.
To meet the requirement of scheduling key rotation, configure Cloud KMS to automatically rotate keys on a regular schedule (e.g., every 90 days).
Control the region where the keys are stored by selecting the appropriate key ring location during key creation. This ensures compliance with data residency requirements.
Cloud KMS provides low-latency access to keys, ensuring minimal impact on data access performance.
Reference:
Cloud Key Management Service Documentation
Encryption at Rest in Google Cloud

https://cloud.google.com/blog/products/g-suite/7-ways-admins-can-help-secure-accounts-against-phishing-g-suite
https://www.duocircle.com/content/email-security-services/email-security-in-cryptography#:~:text=Customer%20Login-,Email%20Security%20In%20Cryptography%20Is%20One%20Of%20The%20Most,Measures%20To%20Prevent%20Phishing%20Attempts&text=Cybercriminals%20love%20emails%20the%20most,networks%20all%20over%20the%20world.