1. It's a good training to exercise with UI, You will need it.
2. An other source of inspiration could be useful. Read it and You will find also some regulations (riser height, recommended outcome, angle of the stair, etc).
3.

If anyone can give guidance on importing, resizing, positioning and displaying objects in a j3d display canvas

I suggest for inspiration to study the code of:
-Modify posture (SH3D)
-Modify opening (SH3D)
-Modify furniture (FurnitureLibraryEditor)

4. You will have also to generate 3D objects (read Export as new furniture & Shape generator plugins)