I am pulling my son out of public school and have already written letters of intent to withdrawl. My question is should I also write one to the school board as well?

There's no need to write one to the school board - just the superintendent's office and the school of enrollment.

If, however, you want the board to know why you're withdrawing, it might not hurt. ;-)  But legally, you don't have to.

You shouldn't have to.   You've researched homeschool laws in your state?

This site will give you a good breakdown on what you're required to do: http://hslda.org/