Hi Capt_buck!
Good questions, and it's cool to see you really diving into the system.
In terms of scale, I've found that the Pit of Mirrors can vary a lot. Sometimes actions spiral out of control and twists introduce new dangers that need to be resolved. I've had folks get lost on the way there or stalked by the jungle cat, or caught in the vines. I've also seen groups come up with clever ways to avoid problems and they fly through it in a few turns.
One thing that can slow the pace of a game without adding obstacles or forcing a roll: taking more time for questions and descriptions. Really dive into the sounds and smells of the abandoned lab, ask about goblins past experience with weird creatures, about how they do something, about what they want out of a situation. I find that spending more time 'in the fiction' can add a lot to play.
When players fail an action more than once, it can be useful to add new threats. The danger for fleeing a burning lab could be that the acting goblin gets pinned under falling debris, or the adventurers come down the stairs to attack. Ideally failing means that you aren't in the same position as you were before the roll. That can keep a desperate scene lively and dynamic.
I agree that small things, without meaningful stakes (like going up and down stairs) doesn't need to be a roll. Save it for the big stuff.
The orb making light/ the ooze being harmed by light is an intentional relationship. Cool to hear you found a dramatic moment there.
I love the image of the tiny ooze dragging a goblin around from inside its guts.