Venting low slope roof – GreenBuildingAdvisor

I am building shed roof design in zone 6 maine with trusses, double stud design (2×4) blown in cellulose, two story house.

-low slope 1:12 roof

-standing seam metal roof

-high temp synthetic roofing underlayment

-5/8″ APA sheathing, engineered roof truss system

-create a 1.5″+ air gap at top for venting with Accu-vent product

-22″ deep blown in cellulose for R74

-Siga Swiss Majrex 200 at truss bottoms – taped as ceiling air barrier and installed prior to erecting second floor interior partitions

-2 5/8″ (half ripped 2×6) strapping installed on edge at 16″OC installed perpendicular to trusses supporting Majrex200, strapping creates mechanical chase possible Rzr style lighting fixtures

-1/2″ GWB ceilings throughout.

On previous post someone mentioned accuvent not advisable as not permeable.  However I am seeing articles by Martin holiday that specify using on site created ventilation space or accuvent.  But 2″ gap is preferred. 

Question

1. Is accuvent good for my setup since it’s 22″ deep cellulose?

 2.  Do I need a permeable vent?

3.  Is it better to instead not have any ventilation?  

4.  Do I need dense packed or better to just blow in at medium packed since slope 1:12?  

5.  Any other recommendations