My suggestions would be:

1. Every user has a username and password stored in the database in a table, password is encrypted
2. The username and password for the database as a whole is for your eyes only.
3. Use a templating system, I suggest the Template Toolkit or HTML::Template.

MySQL is fine for this task. If you want to consider other database engines then I would recommend Postgres. You can find out more about via a mirror found here.

I'd also read up on Ovids CGI tutorial..

Hope that helps
Simon