Volume Deletion

Depending on the data stored and your retention policy, What I usually do is take a snapshot, make sure I include my notes on the snapshot and then delete the volume in available state, once its out of my retention band I remove the snapshot. If you are not sure on the data you could mount it on a worker Ec2 to review the contents too. That way it doesn't hinder production.

Hi.

YES, Given that the volume does not contain any sensitive/important data. You can perhaps create a snapshot of the volume to serve as a backup and further archive the snapshot should you not require the data immediately.

Amazon EBS Snapshots Archive offers up to 75 percent lower snapshot storage costs for snapshots that you plan to store for 90 days or longer and that you rarely need to access.

But in general when a volume is in an available state it simply means that it is not attached to an instance and therefore can be deleted.