I would definitely keep the "user-serviceable parts" stored in a database. Allowing users to directly edit static webpages (i.e. files on your server) would need you to implement a locking system to avoid nasty race conditions. Database servers have this service already built-in. You could then write a number of templates for the different types of pages you have and let the server combine the fixed parts of your pages with the user-written parts.

Checking the user input for potentially dangerous constructs is still necessary, but since the user-written parts are (safely) stored away in a database, you don't have to parse your static files to find the parts which were user written.

An obvious framework for such a system is IMHO Catalyst.

On second thought, it is a bit WIKI-like what you are trying to do, so you might wish to look into that.

On third thought, it is not much different from what we do here at PerlMonks, so perhaps the Everything engine is your best bet.