Most sites could run on a single mid range machine. Top 500 sites could run on a small cluster of less than 10 machines. You have to balance work to external eg

Most sites could run on a single mid range machine. Top 500 sites could run on a small cluster of less than 10 machines. You have to balance work to external egress to intracluster bandwidth while accounting for your total random IOP budget. A well tuned monolith is a beautiful thing.