I have not seen such a plan.

If I were to do it I would first look at the document templates and try to divide them by function, perhaps putting them in separate sub-folders. To the extent possible, I would base them on the same template(s).

Then I would look at building blocks and macros. How would they be related to one another. Ones that work together should be in the same global template. I like to modularize my global templates so that they do not get overwhelming. I can work on one at a time. If any QAT modifications are being used, they should be stored in the same global template that contains macros or building blocks related to them.

Style Sets:
Note that Style Sets consist of only the styles in the Quick Styles Gallery.

You can pick those before you save a style set.

For the ribbon modification, I worked with Greg Maxey to set up the dynamic ribbon menus. I would recommend seeing if he would consult with you on it. It will save you a lot of time. Here is my favorite book on the subject.
RibbonX: Customizing the Office Ribbon by Robert Martin, Ken Puls, and Teresa Hennig


Do not use the interface's method of customizing the ribbon; use XML. The interface method is limited, it is very difficult to transfer to other users. It is OK for an individual user, but not for an enterprise. This was not, for me, a minor undertaking.



AutoText
To me, a dinosaur I guess, Auto Text remains the key building block. I use AutoText to hold key data about my office, names, addresses, phone numbers. I use AutoText fields in many of my templates that pull those in from one global template. That way, I can update all of my templates by making changes in one file.


You will want a training document/manual.


Many of my global templates are written as help files for the functions in that template. Take a look at my MacroButton Prompt Add-In and Random Text Add-In for examples of how this works. Each has a Help button that creates a new document based on the template to explain things. If I modify a function, I change the text in the global template.

Keep in mind, I am a lawyer, not an IT pro.