Contact your County Board of Elections or Secretary of State to answer any questions that are jurisdiction specific.
In Ohio: No, you can leave as little or as much blank as you so choose. Your full ballot will be tabulated regardless. I do not know of any jurisdiction with a contrary law, but that means nothing.
There's never a good answer to your question about unbiased information about candidates... I suppose you could check on Public Information Request policies in your state, request information from the various agencies from which you wish to collect information about that candidate, and draw your own conclusions...