If you're deciding between applying plaster or drywall, drywall tends to be more economical and less labour intensive, but plaster is more effective as a sound barrier. Plaster walls also tend to be more durable compared to drywall, but it requires special training and skills to apply it.
Two attics. Everything removed, then prepped (I.e. boots over pot lights), foam-sprayed, and insulation blown in. We didnt anticipate this particular expense when we purchased this old house, so the price was a blow, but its going to be worth...