(8) EC2 instances in stopped state, is there any cost footprint when in this state?

Yes, there is still a cost footprint associated with EC2 instances in a stopped state, even though you are not charged for compute usage. Here are the key points to consider:

1. EBS Storage Costs: When an EC2 instance is stopped, you continue to incur charges for any attached Amazon Elastic Block Store (EBS) volumes. The storage costs for these volumes persist regardless of the instance state.

2. Elastic IP Addresses: If you have associated Elastic IP addresses with your stopped instances, you will continue to be billed for these as well.

3. No Compute Charges: As you correctly mentioned, you are not charged for compute usage when the instances are in a stopped state.

4. Minimal Data Transfer: While stopped instances don't typically incur data transfer fees, there might be minimal charges if there's any data transfer related to the attached EBS volumes.

5. Quick Restart Capability: Keeping instances in a stopped state allows you to quickly restart them without having to recreate the instance, which can be beneficial for certain use cases.

It's worth noting that if you want to completely eliminate all costs associated with these instances, you would need to terminate them rather than just stopping them. However, termination would delete the instances and their root EBS volumes permanently.

If you're looking to optimize costs, you might consider implementing a policy to automatically delete stopped instances after a defined period of inactivity, especially if these instances are no longer needed or are part of development environments that are used sporadically.
Sources
Amazon EC2 instance state changes - Amazon Elastic Compute Cloud
Community | EC2 cost optimization:15 ways to save on Amazon EC2
Amazon EC2 instances - Amazon Elastic Compute Cloud
Troubleshoot Amazon EC2 instance termination issues - Amazon Elastic Compute Cloud