slight movement of an automatic when parking without using the parking brake is perfectly normal.. you are replacing stuff that did not necessarily need replacing. and for the record, aftermarket axles for a Subaru are garbage.
as for the parking brake, you may need new parking brake shoes and maybe a new cable, but i would bet shoes for sure. they are typically ignored by most when doing brakes because they are not a part of the normal brake system on a car with disc brakes all around, which your Outback should have.. the parking brake is located inside the rotor cap on a car with all disc brakes, typically on the rear - completely separate from the normal brakes.