jonr,
Perhaps I mis spoke: When I said seal up the attic, what I meant is to seal the living space from the attic space, not seal up the soffits and such. Yes, attic space needs to breathe. But it is important to seal the living space from the non-living space
Air Seal and Insulate with ENERGY STAR : ENERGY STAR
On cellulose, your comment is why I said seal up the attic from the house. Cellulose doesn't seal up air movement until it is packed dense, about 2.5 lb / cu ft which you can't achieve with just loose fill, gravity settled, hence the emphasis on the GreatStuff foam.