AWS Credentials - What are multi region user/role management best practices?
Start by reading this: https://docs.aws.amazon.com/IAM/latest/UserGuide/best-practices.html

Those are best-practices and do not take into account business policies.

I don't think having one account per region is more secure than having policies scoped by regions. In cli, you will have to specify the region in the command anyway (not sure if AWS cli uses a default region if you don't specify one in your credentials file).