Well I've been playing it some more, this time on Hard. I'm nearly 40% through and have yet to kill any non target enemies or be detected. Stealth is seeming easier than my Normal run just due to finding routes I wasn't aware of. Not sure about the scoring system though. Is it impossible to get Silent Assassin on levels that don't have a kill target? A lot of sub levels I'm scoring Specialist on and one level I scored Shadow overall.
I'm at the Orphanage now though, so it's going to be tougher to evade all the goons. Just going to keep looking for unknown routes and things to toss. I'm noticing a lot more environment hazards to use, but some I had to leave for another run through. A couple of them at the New Year's festival seem like they might be interesting, especially one involving what appears to be intimate shock treatment. LOL