Explanation
Creating a manual cluster of computeinstances, and Writing custom scripts that will monitor your solution are not valid ways to ensure fault tolerance at all. Also, Performing Data Integrity check when using OCI File Storage Service is not valid since OCI takes care of it.
Therefore, we areleft with:
1) Using multiple OCI Availibility Domains (AD), where available, to deploy your solution - Which is excellent because we have multiple AD's so that if one fails, we have a backup AD!
2) Ensuring your solution components are distributed across OCI Fault Domains - So that we can protect our deployment against unexpected power failures, AD failure etc.

Correct. The IAM service feature that enables instances to be authorized actors (or principals) to perform actions on service resources.

Data Security In Oracle Database Classic Cloud Service databases, data security is provided for data in transit and data at rest. Security of data in transit is achieved through network encryption. Security of data at rest is achieved through encryption of data stored in database data files and backups. >>> Data in Oracle Database files, including backups, is secured by the use of encryption implemented through a key management framework. Security of data across the network is provided by native Oracle Net Services encryption and integrity capabilities.

What is Object Storage?
* All data, regardless of content type, is managed as objects
* Each object is stored in a bucket. A bucket is a logical container for storing objects
* Objects are stored in a single, flat structure without a folder hierarchy. This means that accessing individual objects is fast and easy
* Each Object is composed of object itself and metadata of the object. T his makes it easier to index and access data
* Object storage is quite common in cloud based storage scenarios with very high scalability and reliability
* While files and blocks are generally available to an operating system (by mount operation), object storage relies on standard HTTP verbs

Reference: https://docs.cloud.oracle.com/en-us/iaas/Content/Balance/Concepts/balanceoverview.htm