My suggestion is to look around and try to learn from what was already said here at the Monastery about this topic; for example, you could start from these nodes:

• Building large Web sites
• CGI/Mod Perl Application Design philosophy - which way do we go?
• Web application frameworks / experience with CGI::MxScreen
• OO CGI Engine
• OO Perl & RDBMS Strategy Question
• Web presentation patterns, MVC, and reinventing the wheel

These nodes aren't an exact answer to your question, but will give you some hints. Another solution is to study what other people has done, for example look at chapter 8 of Mason Book or some of the projects listed few days ago at Large perl app source code to learn from. There are also two articles written by perrin that could be useful to make some choices for your project: Choosing a Templating System and Building a Large-Scale E-commerce site with Apache and mod_perl. Finally, there is a list of Web Application Development Frameworks on princepawn's home node that you may find useful.

HTH, Valerio