You can deploy to a different project by using -project flag.
By default, the service is deployed the current project configured via:
$ gcloud config set core/project PROJECT
To override this value for a single deployment, use the -project flag:
$ gcloud app deploy ~/my_app/app.yaml -project=PROJECT
Ref: https://cloud.google.com/sdk/gcloud/reference/app/deploy

Best practices for persistent disk snapshots
You can create persistent disk snapshots at any time, but you can create snapshots more quickly and with greater reliability if you use the following best practices.
Creating frequent snapshots efficiently
Use snapshots to manage your data efficiently.
Create a snapshot of your data on a regular schedule to minimize data loss due to unexpected failure.
Improve performance by eliminating excessive snapshot downloads and by creating an image and reusing it.
Set your snapshot schedule to off-peak hours to reduce snapshot time.
Snapshot frequency limits
Creating snapshots from persistent disks
You can snapshot your disks at most once every 10 minutes. If you want to issue a burst of requests to snapshot your disks, you can issue at most 6 requests in 60 minutes.
If the limit is exceeded, the operation fails and returns the following error:
https://cloud.google.com/compute/docs/disks/snapshot-best-practices

https://cloud.google.com/logging/docs/audit
Data Access audit logs Data Access audit logs contain API calls that read the configuration or metadata of resources, as well as user-driven API calls that create, modify, or read user-provided resource data.
https://cloud.google.com/logging/docs/audit#data-access

App engine is a regional service, which means the infrastructure that runs your app(s) is located in a specific region and is managed by Google to be redundantly available across all the zones within that region. Once an app engine deployment is created in a region, it cant be changed. The only way is to create a new project and create an App Engine instance in europe-west3, send all user traffic to this instance and delete the app engine instance in us-central.
Ref: https://cloud.google.com/appengine/docs/locations