Background checks and fingerprinting for new employees

My questions involve background checks for potential new employees, fingerprinting, developing policies, procedures, and best practices.

Do background checks, fingerprinting, etc., need to be done for all positions? Does it need to be posted in the job advertisement that there will be a background check for the successful candidate or all finalist applicants? Can the background check need to include a financial check and a legal check?

And tangentially, am I correct in my assumption library staff are not considered mandated reporters? Are there guidelines for this as well.