We are currently in the process of building a Tableau Style Guide that will be distributed to anyone using Tableau in our company. The style guide will cover everything in the process including data connections, extracts, scroll bars, fonts, colors, sizing, filters, actions, and even upload and access policies on Tableau Server. Obviously not every company needs something this in depth, however, we have discovered that some topics which are inherent to current Tableau users are helpful to include in the style guide for new users or even new employees. You seem to be looking for more of a "policies and procedures" document on the actual data and integration with the server, and this could easily be something that is covered in your "UR Tableau Style Guide."
There are many examples of style guides online that are very easy to find in order to help find the best topics to cover for your company. While going through some examples we were able to customize some of their ideas or even branch off with a few of our own new ideas. I included a link below to a guide that comes up first in Google made by Oxford University.