1. Is the scorpion taller than 5'? Would it have a hard time fitting in this room with the low ceiling?
Even large scorpions are fairly flat, so it could fit. It could probably even use its sting
2. Does he think the scorpion's "frantic" behavior is directed at him? He waves his (invisible) arms to see if the scorpion reacts to his movement.
It does not react to his movement, but can probably sense him in other ways
3. Does the barred door look like a normal door, with doorknob and hinges? Or is it more like a portcullis that would be raised by some mechanism?
More like a portcullis
If nothing bad has happened yet, then Franklin takes out his crowbar, reaches up and taps the 5' ceiling (to verify whether or not it's solid) then reaches down and similarly taps the floor.
The ceiling and floor seem solid