A) during staging step (after encounter card flip) I'm only looking at the "when revealed" text of that card, completely ignoring any potential shadow text??
B) during combat phase (after encounter card flip), I'm only looking at the shadow effect, completely ignoring anything else on the that card???
in other words: the necromancer's reach (core 93) does nothing during combat???
Yes and yes.
C) can I defend with wandering took (core 43), assigned damage to him (something like old MTG 'damage on stack rule') and than give took to other player to reduce my threat?
Yes, assuming the took survives the attack.