Least Privilege: Always give your users the minimum amount of access required.
Create Groups: Always create groups and assign users to groups. Your users will automatically inherit the permissions of the group. The group's permissions are assigned using policy documents.
Secret Access Key: You will see this only once. If you do not save it, you can delete the Key Pair (Access Key ID and Secret Access Key) and regenerate it. You will need to run aws confgure again.
Absolutely Never use just one access key: Do not create just one access key and share with all of your developers. If someone leaves the company on bad terms, then you will need to delete the key and create a new one and every developer would then need to update their keys. Instead, create one key per developer.
Never store your Access Key ID and Secret Access Keys in GitHub. People have written scripts to scan for these.
You can use the CLI on your PC. You can install the CLI on your Mac, Linux, or Windows PC. I personally use S3 to store all my files up in the cloud.