I would guess scorpions do stop working at some range. Testing weapon and magic range (
here) I found that enemies not shown on the mini-map are not shown on-screen if you move the screen focus over (enable Caps Lock or hold down the Shift key). Basically, that meant a range of a couple screen height/widths away from the character.
If there are traps (and presumably ressurected or summoned creatures) active, the game does extend the distance it controls their actions, but I am not sure by how much, or how long.
If you ressurect a few creatures in a confined area, release a scorpion and teleport away the ressurected creatures will turn hostile. Approaching the place on foot, you may be able to determine how close you need to be for the scorpion to start attacking, if it did not do so right after you left.
The helm and breastplate from the council hall are potentially pretty good. I used both for awhile until I got the dragon armour (the dragon armour was better, but it wasn't a huge difference).
The bow dealer in the Dark Forest elven village sometimes sells mythril armour, which has no strength requirements, but can have a high armour class (not sure how likely they are to have various bonuses, though).
