Grid 0?

What grid set up is best? How does it affect autohinting?

The best grid setting depends on what you try to do. For regular fonts you will keep it at 1. You may set it to 0 in between if you need to do several transformations.
Higher values a useful for pixel fonts.
You set it to 0 if you have VERY fine details like small rounded corners or thin lines. This might happen in icon fonts.

So, if you have no specific issues, keep it at 1.