Good luck with the blog. I've always found the WHMCS docs to be quite useful, at least for the topics they cover.
That being said, DemoWolf (video tutorial company) recently relaunched and it seems they will be releasing a WHMCS series sometime this year so do keep an eye out on that.
As for your question, they focus on the features they offer but really lack when it comes to customization (which every company generally does in one way or another). I'm referring to: Website design integrations, removing clutter from the order form (header etc) and the more advanced customizations.