Issue 1:
Use boxes to create your own baseboards for illustrative purposes. That way you have full control.
Issue 2:
Apply a textured box to the end of the wall as an illustrative make-up.
Issue 3:
Tricky, but it’s really more of a constructional challenge than a texture problem. Create your stairs using boxes in SH3D, and the texture problem is solved.
Alternative if you are set on making your models with Sketchup: Get a program like f.i. Blender or Verto Studio 3D that can unfold your model and fix your texture coordinates.
Issue 4:
Download this file:
Walls sh3d
Best of luck,
Cecilia