In addition to other requirements under law, a state agency shall:
(1) adopt rules of practice stating the nature and requirements of all available formal and informal procedures;
(2) index, cross-index to statute, and make available for public inspection all rules and other written statements of policy or interpretations that are prepared, adopted, or used by the agency in discharging its functions; and
(3) index, cross-index to statute, and make available for public inspection all final orders, decisions, and opinions.