Perhaps I can help.
You mentioned fresh install, if you have not added the email information to the Global properties file, please do so.
I know how to setup SMTP for sending emails form Alfresco, and can provide more info if you want.
At our library we did pretty much want you are trying to do.
How we did it was with groups and role based security.
I created Groups named for the different sites, and Groups for the site as a Site Admin (so two Groups per site).
I then created the sites, and added the Groups (for the site) and assigned privileges to the groups.
I then created users, and in the user setup, added the appropriate groups to each user.
So no emails, no joining, just good to go when they login.
The trick is rembering to add the correct groups to each user, and rember a single user can have many groups.
Does this help? If you want more on what or how we did it, just ask.
Good Luck,
Mike Chase