Insulation challenge - exposed wood beams with 6" tongue/groove slats on top form ceiling with attic above
Your goal here is a significant improvement in energy efficiency without causing any unwanted side effects, such as moisture buildup in the wrong places. With that in mind, I'd keep it simple. 


Lay 4 mil poly sheeting right over the existing insulation. Unless the stuff is filtering through your ceiling and making a mess, just leave it alone. Lap joints 2 feet or so. This will provide an effective seal. It's not critical to create an actual balloon out of your house. You just want to eliminate the majority of airflow between the conditioned space and outdoors.
Blow the appropriate amount of cellulose over the poly. 


That's pretty much it. You'll probably need to build a simple barrier around your access port to contain the insulation, and be sure any recessed light cans are rated for insulation contact. Otherwise, don't overthink it.