Cliff notes:

Can I pin up plastic sheeting to the underside of my Rafter joists and than blow in cellulose (and use my old fiberglass batts)- will the plastic act as a vapor/moisture barrier and avoid moisture/insulation issues, or should I put rigid non permeable foam panels between my rafter joists and spray foam the joints-than put up old fiberglass batts and cellulose.
Just using the fiberglass because I'm pulling it out of vaulted ceilings and doing a "tight pack" cellulose fill and I will have a ton left over.

Longer version below.

Just bought a 1985 home with vaulted ceilings and about an R-3 of insulation in the attic-if you don't count the massive air leaks around the return air vents and anything else that goes into the attic space.
The attic floor is 2"X6", and not well insulated with blow in fiberglass- at least where there is insulation.

SO, this is the plan thus far:

Take 1" R-max foil face rigid foam insulation and adhere it to the bottom of the roof sheathing and seal with expanding foam.
Use the fiberglass batts (that are going to come out of the vaulted ceilings) and batt under the R-max rigid foam insulation, I think this will work well, but....

Could I instead place thick plastic sheeting on the roof joists (inner attic side) as a vapor barrier and than blow in cellulose up to the roof sheathing and also use insulation batts? Would the plastic sheeting keep out moisture and keep the cellulose/ used batts dry?
I believe the cellulose and fiberglass batts will keep the cold outside air insulated from the warm/moist attic air, and the plastic sheeting will keep the inner moisture aware from the cellulose and used fiberglass batts

Also, I will be pulling the fiberglass batts out of the vaulted ceiling and "tight pack" cellulose to improve R value and use the tight pack method as a vapor barrier/retardant.

As far as walls-I've gutted my master bath down to the studs-r-11 fiberglass batts-except along the top plate, where there is no insulation for the entire span of the wall from the wall plate to the floor sheathing above.
The plan is to install 2" R-max rigid foam in between the studs (I know, there's going to be thermal bridging) and spray foam around the edges of the rigid insulation for a vapor barrier and than plastic sheeting vapor barrier under the dry wall.
This will create a1.5" air space between the rigid foam and the plastic sheeting/drywall combo.

Any suggestions on my plastic sheeting with cellulose between rafter joists-seems like it would insulate well and have a nice vapor barrier while keeping costs minimal.
Also, will there be a moisture issue between plastic sheeting installed underneath drywall in a bathroom and rigid foam in the wall cavity?

Thanks all.