On the insulation, the vapor barrier(paper) goes toward the heated space, up in your case. No additional barrier is needed. Most codes require 5/8 firecode drywall. Some areas require double sheets. Your building department should be able to tell what is required.
How much insulation is in the ceiling??? More is better but it should not be packed tight. This is the last time you will be able to fill any gaps or openings in the insulation. Check it over thoroughly.
How much insulation is in the ceiling??? More is better but it should not be packed tight. This is the last time you will be able to fill any gaps or openings in the insulation. Check it over thoroughly.