What are the necessary components of the board?

Diversity of perspective,  industry experience and or customer access. Think about conflict of interest and broadening your base. 

Two cautions:

Industry experts become progressively less useful over time

In some instances if you hire a board member from a key customer the deal flow can dry up due to conflict of interest.  Consider the person for an advisory role. 

Early on:
A mentor/coach that you can work with in a safe zone.

One or two founders on the board usually it is the CFO and the CEO then eventually but not always becomes one founder (CEO).