Custom templates don't have a way to provide descriptions or best practices. As an organization creates more custom templates the only way to understand what they are for or how to use them is via oral history or links in the created document.
Loss of knowledge over time and wasted effort creating documents from incorrect templates.
Provide a mechanism for defining descriptions, best practices and an image in custom templates.
Custom templates would have a See details button in the explorer that would display the description as well as any defined image
Once created, the Best practices panel would be available to show those.
In short, create a parallel experience for built-in and custom document templates.