Deploy your application to App Engine using the gcloud app deploy command. This command automatically builds a container image by using the Cloud Build service and then deploys that image to the App Engine flexible environment.

Database Migration is the right one to use: "Simplifying migrations to Cloud SQL. Now available for MySQL and PostgreSQL migrations, with SQL Server coming soon." Since the customer also doesn't want to manage their own database installations in the future, Cloud SQL is the best option.

https://cloud.google.com/database-migration

you can get a 57% discount by agreeing to commit to a 3-year contract. Any usage over the commitment will just be billed at the standard rate. Since they only need 300 CPUs 30% of the time, will pick answer C so that we are not paying usage off 300 CPUs all of the time. This gives us a discount of 57% for 200 CPU's, huge cost savings.

Reference:
Cloud Bigtable is a sparsely populated table that can scale to billions of rows and thousands of columns, enabling you to store terabytes or even petabytes of data. A single value in each row is indexed; this value is known as the row key. Bigtable is ideal for storing very large amounts of single-keyed data with very low latency. It supports high read and write throughput at low latency, and it is an ideal data source for MapReduce operations.
Bigtable is exposed to applications through multiple client libraries, including a supported extension to the Apache HBase library for Java. As a result, it integrates with the existing Apache ecosystem of open-source Big Data software.
Bigtable's powerful back-end servers offer several key advantages over a self-managed HBase installation:
Incredible scalability. Bigtable scales in direct proportion to the number of machines in your cluster. A self-managed HBase installation has a design bottleneck that limits the performance after a certain threshold is reached. Bigtable does not have this bottleneck, so you can scale your cluster up to handle more reads and writes.
Simple administration. Bigtable handles upgrades and restarts transparently, and it automatically maintains high data durability. To replicate your data, simply add a second cluster to your instance, and replication starts automatically. No more managing replicas or regions; just design your table schemas, and Bigtable will handle the rest for you.
Cluster resizing without downtime. You can increase the size of a Bigtable cluster for a few hours to handle a large load, then reduce the cluster's size again-all without any downtime. After you change a cluster's size, it typically takes just a few minutes under load for Bigtable to balance performance across all of the nodes in your cluster.

VM instances that only have internal IP addresses (no external IP addresses) can use Private Google Access. They can reach the external IP addresses of Google APIs and services. The source IP address of the packet can be the primary internal IP address of the network interface or an address in an alias IP range that is assigned to the interface. If you disable Private Google Access, the VM instances can no longer reach Google APIs and services; they can only send traffic within the VPC network.

https://cloud.google.com/vpc/docs/configure-private-google-access