I agree. Depending on the type of hypothetical website, you could expect that most traffic comes e.g. during the week at business hours, or maybe in the evening after work. You need to design for that spike in workload (maybe 10x?)

There was a story recently about running the workload of Twitter from a single machine: https://news.ycombinator.com/item?id=34291191

Yes - possible but no redundancy, difficult maintenance