You always need a leader who sets the vision. Beyond that top-level board or exec, sure, you can outsource everything else. There are pros and cons to it. If I were you, I'd go research the history, successes, and failures of various consulting models before you try to start something new. Because it absolutely can work, but if you don't find the giant shoulders to stand on, you are ignoring decades of lessons learned and will sound like someone who doesn't know their own industry.