4 people is the bare minimum for realistic 24/7 support. Even if you just do "on call" support outside office hours, making sure someone (capable) is available every weekend and at o-dark-thirty every day is difficult with less than 4 people.
(Says a guy who spend too many years as part of a 2 or 3 person sysadmin team...)
Maybe I'm insane or overly optimistic or both. Designing things to bend and not break is really difficult and time consuming. "Thanks Captain Obvious! You are so insightful!" No, I know, but I'm going through the cutting-of-teeth ritual now so these kinds of things are on my mind.
The key point is, if your business model depends on more user usage ie, more uploads more money (on a 60 server scale), you would like to have someone standby all the time.