An advisory board is an informal group. This is not a board of directors. It is a group of mentors. The group has no financial interest in your firm. This is a group of outside advisors who share their knowledge to help you be more competitive, think strategically and offer specific advice in key skill areas.
The benefits of an advisory board include: setting aside time to think strategically, obtain feedback and insights from outside the company, and gather information and expertise from peers who have knowledge in different areas than your own. In general, a three to five person board will likely meet your needs.