How to allow a role to add user without adding user name, password, roles, etc
It sounds like these people you're adding should not be added as users to the system.  You should only add users if they are going to be actually logging into Drupal.

If you're just trying to keep a record of clients then you should store them as nodes.  Configure a new content type called something like "customer" and add and configure the appropriate fields that you wish to store about these customers.