To edit the user creation defaults you can use the 'Edit defaults' dialog, which is accessible via the menu File->Preferences. There you may change the defaults that are used when creating a new user: Shell, Home Directory (or home directories volume). Also, you can chose whether to make a home directory on 'create' or not, to copy a skeleton to the home directory or not. You can also enable 'User Private Group' mechanism, which creates a new personal group with the creation of a new user, and removes the personal group when the user is removed.