"Is the 4 mil plastic on the exterior side of the studs acceptable for my application?"
You need to use an air barrier like Tyvek which allows gaseous water vapor to pass through from the inside to the outside while keep exterior air out.
Using 4 mil plastic creates a 'double vapor retarder' wherein water vapor can get stuck between the kraft faced paper on the fiberglass and the polyethylene sheet.
The result will be water trapped in the wall cavities causing wood rot and possibly mold growth.
For your climate, vapor retarders whould only be installed on the warm-in-winter side....over the studs...under the drywall and no where else.
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