Will the following vaulted ceiling structure cause moisture problems?
Vented shed roof 20′ long, attached to house using 1/2 of a scissors truss tied to 2X6 house studs.
Trusses are made of 2X6 top and bottom members, 2X4 centers, plywood sides glued and screwed, 4/12 pitch outside 3/12 inside, placed over the wall with 2′ overhang & full 11″ height over wall plate.
Trusses provide 24″ overhang with fully vented aluminum soffit.

Starting from the shingles moving toward the inside:

-1/2″ OSB on top/outside of trusses placed on 16″ centers. 16# felt, dimensional 30 yr asphalt shingles.
-Cor-A-Vent air vent outlet at the top of the the 20′ shed roof trusses up against the outside of the house for a full vent from soffit to top of shed truss on every bay.
-1/2X2 OSB cleats nailed to inside lower edge of top/outside 2X6 of trusses with 1/2″ fiberboard nailed to cleats below and caulked to trusses. This creates a sealed 5″ air passage above fiberboard and below roof OSB sheathing.
-1/2″ Foamular on inside/bottom 2X6 of trusses, all seams taped, with 5/4X3 strapping boards below it, perpendicular to trusses on 16″ centers with 3″ screws.
-3/4″ Foamular over 1/2″ foamular and between 5/4X3 strapping boards nailed to bottom of trusses with 2″ plastic caps.(3/4″ Foamular is just above strapping board lower surface now, so not exerting downward force on drywall with weight of dense packed cellulose)
-Cavity between 1/2″ fiberboard and 1/2″ Foamular is dense packed with cellulose. This space starts at 6″ thick over outside wall and grows to about 24″ thick at the house due to the difference between the inside and outside pitches of the 1/2 scissors trusses. (most warm air will be at high ceiling near house)
-6 mil plastic vapor barrier over entire ceiling, joints taped.
-1/2″ drywall over plastic vapor barrier.
-Latex primer and paint.

The idea is for the assembly to dry to the outside in case there are any air leaks from the inside. The fiberboard serves as a wind baffle to the cellulose insulation, and is very vapor permeable. The cellulose was chosen for dense packing in the 1-1/2″ truss areas covered with plywood as well as all the areas of the webbing in and between the trusses. The 1/2″ Foamular is just to contain the cellulose and be able to tell when a cavity is full (bulge). The 3/4″ Foamular is just to fill the void between the strapping. The plastic caps are to help support the slightly sagged 1/2″ Foamular which is supporting the dense packed cellulose through the 3/4″ cellulose. The 1/2″ Foamular provides a thermal break between the inside and the outside.

This system would be (at the outside wall) for R calculation:
1/2″drywall
3/4″ Foamular
1/2″ Foamular
(Thermal break)
6″ densepacked cellulose
1/2″ fiberboard

and the thickness of the cellulose would get greater as you get closer to the house.