I have used this mod a little bit, and it looks pretty good.
I would agree that ramps would make more sense than stairs.
If you have to have stairs, go with dirt ramps with simple wooden steps
On the subject of cave ins.
I happened to think about one mod I found a while back (Midas?) that might give interesting inspiration for cave ins.
The mod had weapons and bombs that created 'gold', in chunks and bits.
I also recall a mod (forget which one) with a weapon/tool that fired bricks.
It occurred if this could be done with gold, or bricks, why not try something with dirt and clumps of dirt or even rocks?
Would it be possible to do something similar to what is achieved with the Midas mod, and the brick shooting weapon? But instead have dirt particles in addition to chunks/clumps of dirt and little bits of rock be generated by what might equate to one or more invisible downward aiming 'sprayers'?
The chunks of dirt, and any 'rocks', could have a fair bit of weight to them, to add a bit of impact to anything caught in the cave in, or at least knock down actors to increase the risk of them getting buried alive.
It might make sense to have it be a sequence of sorts, with a central point having little come down before adjacent points then be created to start to dumped out dirt as the middle one then has a rapid increase in speed and volume of dirt, dirt chunks and small rocks followed by the adjacent ones then having the rapid increase.
Maybe also a basic, invisible 'digger' effect aimed upward, to give the appearance that the area above had collapsed downward.
The only downside might be a bit of lag, but it might be able to provide a somewhat realistic, and potentially deadly, effect without actually tossing in any 'instant kill' particles.
On a related idea, would it be possible to make a few items that might fit in with the style of the modules?
Some 'blocks' of dirt, as a dirt counterpart to concrete blocks, to help full in gaps, or for making basic obstacles.
Also, a module of solid dirt, to help 'patch' possible mistakes when a dirt module misplaced or when accidentally placing the wrong one, or just to add a bit of extra dirt for some reason.
A wall and short barricade of dirt, perhaps with wooden sides. Just something for basic obstacles, with the barricade providing some basic cover
If possible, how about a wooden door/gate of some sort?
Other ideas for traps.
Since there are wooden supports, how about traps that drops lots of lumber/wooden planks (or full blown logs or stacks of support beams) onto someone? Or rip off Indiana Jones, and have one that drops a big (non-rolling?) rock on some poor clone or dummy.
How about a pitfall trap? Could be a place to put a mine or other thing one would not want to fall on, or perhaps be used so an actor falls through and lands in a lower tunnel.
Crates marked TNT... if we are going to have possible mining style tunnels, we might as well toss in old crates of things that explode... perhaps in a cave in area... perhaps it can hold really old, delicate explosives with a 'hair trigger' that might go off with the slightest impact...