There is a lot of value in getting some kind of board of directors or advisory board in place as early as possible. Somebody needs to tell you when you’re messing up.
More importantly, somebody needs to tell you when you’re doing a great job. Without the board life can get very lonely.
Your ability to get the right kind of people to sign up for this is also a good early indicator for your ability to attract employees, customers, investors, partners.
Personally I’d recommend a three people setup at the beginning, minimum two, maximum four.
For a more systematic view on this topic you may want to look at Brad Feld’s book on Startup Boards.
olivergajek 
So true! I can’t tell you how much our board helped me during the last year. The tricky part is to find the right people for your board. A wise man told me once, that if they ask for money upfront it’s a bad sign. But what is a good sign? Maybe it’s wise to figure out If they believe in you as a person and want to see you succeed, maybe it’s just complementary skills and maybe it should be both. Brad Feld’s books are definitely a good read, no exception. Thanks for the post Oliver. Greetings David
If and how and when to pay your supervisory or advisory board members is a good question and there are no easy answers. At the very beginning you don’t really have cash to spend. Pure volunteerism, on the other hand, is also not sustainable for many potential board members. So you’ll have to be creative about deferred or success-based cash compensation (in case the relationship is not necessarily long-term) or stock awards with a long-term vesting schedule (in case you want them to stick around).