As said already, you install a catwalk (per code; width) high enough to get full R-value to the unit from the scuttle hole. Cover exposed Romex within 6' of the attic access from walking on, per code. "Hanging from the joists" or maybe rafters- make sure they add additional vertical supports to a bearing wall below to carry the additional roof loads. Be sure your drywall can carry the additional insulation weight; https://docs.google.com/viewer?a=v&q...h3VLQNBaXp54rA
And if plaster/lath, the ceiling joists are able to take the weight as they are already at 8#per sq.ft., the extra weight may over-span them.
Air seal the attic now, optimum time- as you will benefit greatly;http://www.google.com/url?sa=t&sourc...wWATQw&cad=rja
Verify the attic ventilation requirements for your location, add more if needed (moisture on framing/exterior ice dams).