How you construct it depends on its purpose. If you want this thing to be a boss fight for N characters with K karma apiece, I'd start it as a cyberzombie, since those are intentionally overpowered to begin with. If you want to play it more realistically, then yeah, I'd probably build it up as a drone.
I'd presume movement would be an easy way to pick it out of a crowd. Human motion is very intricate with all sorts of subtleties that are a pain to simulate; of course, if you want to eliminate this, invoke the Sufficiently Advanced Pilot clause and say it can handle that much processing or whatever.
Aura and essence has to do with being a living creature and not necessarily having a consciousness, from what I understand. (Do coma patients have auras?) There are some species of bacteria that are dual-natured, IIRC (which an AI with enough resources and a suitably sadistic DM could, in theory, load its shell with to disguise it even further, even if a closer examination would probably reveal "hey that's a pile of bacteria not an actual person's aura). So, basically, I'd say no, it wouldn't have an aura or essence because it's an artificial creature, even though it's sentient.
