Some recommendations that I found to calculate number of users depending on the expected number of users are on those threads:
https://groups.google.com/g/edx-code/c/VUaRXqdN3m4/m/dsCpJguPCAAJ
https://groups.google.com/g/openedx-ops/c/_El2M0ifXmc/m/R5vCdGaBBgAJ
Although, the issue of preparing the server for bigger loads and scalability, through external storage, databases and several servers is something to be researched deeply. Let us know if you find any other resources.