After spending all day working on this, I've finished building and importing the basic architecture of the limbo using the modeling program.
This works perfectly fine, except I exported everything with centralized vertices which was dumb of me.
Basically what that means is I built everything, and it was relative to the world origin. When I imported everything, I centred the origins to the geometry which killed the relative positioning that the models would have retained through import, meaning I could align all the geometry to 0,0,0 and everything would be as tightly knit as it is in the original model.
Regardless, the point is that it works.
For floors and accessories, I just run the convex collision tool after import, and that usually provides a good enough collisions model.
For walls, I turn off simple box and simple line collisions, leaving simple ragdoll calculations to provide the collisions.
I'm not sure how the current cover system will work against the static meshes.
Is modeling the map in the modeling program better than creating BSP? Not in all cases, obviously BSP provides culling that static meshes do not, so I'll have to use volumes to block sight.
I'm still not 100% convinced I'm approaching this in the best manner, but again, it works.
If you're trying to create a curved staircase, there are a number of ways to do it.
In Sketchup, you have to find plugins tools that will provide duplicating along a path.
Like this one:
http://www.smustard.com/script/PathCopyCreate a 128x64x16 block, dupe it along the curve.
Another way to do it is to use the curved stair case tool in the UDK, but don't leave it as a BSP construct, else the face count will kill the framerate. You can convert BSP to static mesh and it will be saved in a UPK. This is much cheaper to render, but once you've converted the BSP, it's no longer BSP, so you can't modify it. It's a one way transition.
The last way to do it so build a slope, then duplicate subtractions into the slope, thus notching stairs out. This performs well in render because the stairs are providing only two faces per. When you create a staircase with the staircase tool, there is potentially four to six faces for each step. Multiply by thirty then multiply by two. Ouch.
Man, no amount of planning...