Why Perl? Because my website is written in it, and I need to add features.
I'm not sure what language would be more sensible in general, though people seem to like Python.
As might be expected for any project, my impulse is to buy more books. There seems to be a classic on debugging conveniently called Debugging, but a fast search doesn't turn up anything on the general principles of documentation. Does such a thing exist?
Addendum: mneme very generously wrote my website. These days, he fixes it when it breaks but doesn't have time for development.
Addendum the second: Another possibility is going to osCommerce, free commercial website software with a good reputation, but at the moment, perl seems more interesting.