If you are going to paint, use a 'flat' sheen paint to keep light reflectance to a minimum. Paint color is not so critical as reflecting light. I would also suggest using an exterior paint as they are washable, contain mildewcides, and are generally more resistant to whatever might hit it. Next, cover the ceiling. Open rafters invite dust. If there is a floor above, foot traffic can dislodge it. Get an inexpensive air purifier, that will help with dust control.