In general, one should think that if a building is warmer indoors than the outdoor temperatures for most of the year, a vapor retarder should be used because the vapor pressure from inside is greater. If the building is cooler indoors than outdoors for most of the year, a vapor barrier should not be used on the inside as the vapor pressure is higher from the outside.
If there is occasionally high humidity indoors, a moisture-controlled ventilation system or dehumidifier might be good to install.
When it comes to cellulose insulation, one should follow the manufacturer's instructions.