1) If i do not provide an OPAC login when adding a patron, i am assuming they cannot login.
Patrons can log in with either their login or their card number. You would have to remove the password (or set it to something they didn't know) to prevent them from logging in.
2) Is there a way to disable a patron login to OPAC at any time? What happens if i edit the patron record and clear out the login name?
Setting the opacuserlogin system preference to "OFF" will turn off all login-related features of the OPAC, including the login form and "place hold" links.
3) Is there a way for me to add a patron and defer creating their login till later?
Koha will automatically generate a login name for your patrons based on their name, but there's no requirement that you set the password at the time of patron creation.
4) Anytime i edit the OPAC login, does the e-mail notice with the login and password information get sent automatically? Or is there a way i can trigger them manually?
No, but that would be a nice feature to investigate. -- Owen -- Web Developer Athens County Public Libraries http://www.myacpl.org