Our documentation regarding recommendations are meant to be used as a guideline to give some idea as to how Tableau Server may be configured in different scenarios - Performance Tuning . However, the best answer is typically found through trial and error in each environment and is specific to not only hardware, but the use case. In order to "plan" a configuration of Tableau Server one must understand what the main processes do and conversely must understand how they will impact the use case. Here is some information which will be helpful: Tableau Server Processes
The best way to tune a deployment is to formulate the best configuration using the examples and process descriptions provided then tweak it to what you feel is suitable to meet the needs of the users. Test it. Then adjust. Obviously, this is best done monitoring during heavy use periods and adjusting configuration during maintenance.
In the more recent versions of Tableau Server, the initial installation will auto configure the number of processes to based on the available hardware in a balanced type scenario. An example would be 2 VizQL Server, 2 Backgrounders, 2 Cache Servers and 2 Data Server for an 8 core/32Gb Ram machine.
Just keep in mind, Tableau Server is built to be flexible. As such, it can be balanced or weighted toward a feature (like having more backgrounders to keep data extracts up to date).
Also, if you would like, I am positive your Sales Rep has some resources they can pass your way.