Single IAM Policy for multiple users to access particular S3 bucket.

You can use tags on the IAM users and on the buckets and then create a policy that allows access if the values of these tags are equal, using the same policy for each user. Something like this:

{
    "Version": "2012-10-17",
    "Statement": {
        "Effect": "Allow",
        "Action": s3:*,
        "Resource": "*",
        "Condition": {"StringEquals": 
            {"aws:ResourceTag/Owner": "${aws:PrincipalTag/Name}"}}
    }
}