2: Most AWS setups are sufficiently different that giving specific details here are hard. Can you explain more about which ARN you are looking for? Are you asking about the ARN to use when you create the in the CLI tool, or for the cross-account IAM User?
3: Noted, thank you. I'll make a request that the document gets fixed.
4: Can you explain what you are trying to accomplish? In your setup, do you have more than one AWS app icon in Okta? Or are you asking about apps hosted in AWS?