Definatly agree with telcoguy about the passwords and thats easy, you can control the minimum length for the password.
You don't need to have outcalling turned on for what you want, that is just to notify someone who is away that they have a message. VDN... not really necessary. I think the easiest would be if you have an auto attendant set up and
have a did number coming in to it, they can just enter the ext no. of the audix hunt group.