Service Gateway is virtual router that you can add to your VCN. It provides a path for private network traffic between your VCN and supported services in the Oracle Services Network like Object Storage) so compute Instances in a private subnet in your VCN can back up data to Object Storage without needing public IP addresses or access to the intern

An internet gateway is an optional virtual router you can add to your VCN to enable direct connectivity to the internet. Resources that need to use the gateway for internet access must be in a public subnet and have public IP addresses. Each public subnet that needs to use the internet gateway must have a route table rule that specifies the gateway as the target. For traffic to flow between a subnet and an internet gateway, you must create a route rule accordingly in the subnet's route table (for example, destination CIDR = 0.0.0.0/0 and target = internet gateway).
Dynamic Routing Gateway (DRG) is A virtual edge router attached to your VCN. Necessary for private peering. The DRG is a single point of entry for private traffic coming in to your VCN,After creating the DRG, you must attach it to your VCN and add a route for the DRG in the VCN's route table to enable traffic flow.

Due to the network speed is not good enough and the connection is Intermittent due to the damages caused to the electrical grid Oracle offers offline data transfer solutions that let you migrate data to Oracle Cloud Infrastructure.
You have 2 Options of Data Transfer
DISK-BASED DATA TRANSFER
You send your data as files on encrypted commodity disk to an Oracle transfer site. Operators at the Oracle transfer site upload the files into your designated Object Storage bucket in your tenancy.
APPLIANCE-BASED DATA TRANSFER
you send your data as files on secure, high-capacity, Oracle-supplied storage appliances to an Oracle transfer site. Operators at the Oracle transfer site upload the data into your designated Object Storage bucket in your tenancy.

Explanation
You can change the shape of a virtual machine (VM) instance without having to rebuild your instances or redeploy your applications. This lets you scale up your Compute resources for increased performance, or scale down to reduce cost.
When you change the shape of an instance, you select a different processor, number of cores, amount of memory, network bandwidth, and maximum number of VNICs for the instance. The instance's public and private IP addresses, volume attachments, and VNIC attachments remain the same.

You can configure the Autonomous Database instance as a target database for Oracle GoldenGate. But You can't set up Oracle Autonomous Database as a source database for Oracle GoldenGate.
Recovery Point objective (RPO) of 24 hours and Recovery Time Objective (RTO) of 1 hour
- To provision new VM and restore the production database from the backup on object storage, will exceed the RTO 1 hour
- You can create the standby DB system in a different availability domain from the primary DB system for availability and disaster recovery purposes. With Data Guard and switchover/failover can meet RTO
1 hour.
- RAC Database is not required in this solution. Standalone will be most suitable and cost effective