1) Just have them create an account, and then you can edit their profile in the control panel and under permissions you can add them to the Administrator group.
2) No, that should be a number. It's the userid of the primary admin, in this case your first user that is registerd (#1 is reserved)
As for the avatars directory you want to use a full path. In your case "/home/vintager/public_html/images/avatar/default". Normally it's best to create an entire different directory for these however under thee public_html directory.
