I have a large attic with a ridge vent, but no soffit vents or other vents for air intake. As such, the attic gets very moist and cold/hot. I would like to finish the attic for additional living space. As such, would blow-in insulation be suitable to insulate and seal the attic prior to finishing? As I live in the Northeast, would I need to extend the rafters to get adequate insulation? Also, would I remove the ridge vent and leave in the floor insulation?