Instead of a style guide, might I recommend code reviews? Every week or two, have a different member of the team send out copies of the code they're working on or just completed, along with explanation of what it's supposed to be for. Schedule a meeting for that person to walk through the code, explaining it, and have your developers question what they find unclear or dangerous.
Even if you decide to go ahead with a style guide after starting the code reviews, the style guide will be more effective. First of all, since code reviews are a two-way street, you'll be able to see what your coders do and don't understand and what needs explanation (cf. Abigail's why's). Since reviews are a two-way street, your CGI programmers will have had an opportunity to contribute to the process, so they'll be more likely to go along with it. Finally, code reviews give you an opportunity to enforce your style guide.
Personally, though, I find style guides are usually a Procrustean solution. When I've tried writing them in the past, it came from spending so much time programming the computer that I was trying to program the people around me. I understand where most of these rules are coming from, but I've disobeyed most of them in code that I still consider good. Most style guides are enthusiastically propounded, then studiously ignored.