Your Tableau Account manager can help you with planning and license needs. Feel free to contact Tableau directly for that assistance. In addition, you may want to read - Tableau Server Scalability - A Technical Deployment Guide for Server Administrators | Tableau Software https://www.tableau.com/learn/whitepapers/tableau-server-scalability-technical-deployment-guide-server-administrators?signin=0092730353215cff0d68acbb78e6a695
I hope this helps,
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I agree with Patrick, talk to your account manager. They will be able to get the necessary details to get a baseline on what you need. They will also explain your other questions like license transfers.