HI Anabelle You don't mention it, but if they had to cut off a stud to insert the A/C unit, you will have to build a new box-frame into the opening, which can be a bit tricky if the existing studs are difficult to reach from the opening. If this is something you haven't done, you may have to get a local carpenter, as the studs are probably close to a full 2" X 4", meaning 2X6's will have to be ripped down to the old stud size. The exterior stucco patch should not pose too much of a problem if you have applied stucco in the past. If not, I'd get a local stucco guy to do this fix. The inside repair will be a little more difficult. You probably have lath and plaster, which will require blue board and a base or 'scratch' plaster layer with a skim or 'putty' coat atop that, feathered into the existing plaster. Its the last part that requires some experience and skill, lest it look a bit tacky.
And yes, newspaper was the insulation of choice back in the teens