It depends hugely on what you are doing. At Kickfolio, we needed to think about dev ops and infrastructure right from the start. Kickfolio launched with 13 servers in place (10 Mac Mini's, EC2 load balancers, Heroku front end).
Having been featured on a few large sites, it was enough. We spun up 3 dynos on Heroku for the front end, and in the first week of launch we had gone through a few hundred GBs on bandwidth (not including static assets hosted on Cloudfront).