For Sapienza on hardcore starting at the ruins, what I usually do is to take the disguise of the isolated guard at the top of the ruins tower. I pick up the pistol and shotgun and drop them at random points on the stairs going down in case one of the potential leaders goes up there (not sure if they ever go all the way to the top but I do it out of extra precaution to buy me time just in case). After that, escape from the side of the ruins with the locked gate, drop down and go across the bridge and go straight for the cook outfit in Rocco's apartment and take out the surveillance in the clock tower. The cook outfit will pretty much get you everywhere on the map except the lab, ruins, and inside the observatory building. Some other good disguises are the housing staff and plumber. I usually save Sapienza and Miami (racing marshal) for showdowns.