Your question seems to have little to do with the PostgreSQL-ness of the application and more with the web-ness of it. Other than that, it seems to be a standard CRUD (create, read, update, delete) application.

While I have not had much success with CGI::Application (and I attribute it to my own obtuseness -- dragonchild very kindly and patiently explained to me the basics of CGI::App, and while his explanation seemed to make sense, I got bogged down by myself), it seems to be a good framework for organizing code.

Since you are going to be dealing with user-specific issues, you would probably need CGI::Session of sump'n like that to manage sessions.

CGI::App (or any other such framework) will allow you to create separate CRUD-specific modules and organize them in separate directory hierarchies.

Size of the app is irrelevant here in my view -- bugzilla may or may not be a good starting point as it might be too complex, but then, it might also be a good study.