Your question would require quite a long answer. General specs of the different formats, you can find many places online. Usually the files needed will contain the geometry and additional colour & texture files. (For transparency in .obj format, you could test different renderings with a combination of transparent graphic file and transparency in the .mtl file - see this thread and this thread).

As for the SH3D specifics you may want to have a look at the FurnitureLibraryEditor (see download page) which will allow you to supply additional model information.

For instance: .obj (and other import) files do not support some more advanced features like window/door cut-out, but this can be added with the FurnitureLibraryEditor. If you need light sources in the model and other advanced properties, you may just need to dive a little deeper into the file specifications (see Sourceforge docs).

An SVG mini-manual - specially from page 9 on - may possibly also give you a hint or two on how to add extra (SH3D specific) qualities to your models.

As for the camera / light you use in your 3D modelling software to produce a rendering, I guess you will need to substitute with light sources and view angles in SH3D - or am I misunderstanding what you are trying to do?

Best modelling software? What you feel most comfortable with [:)] Blender is very good software once you get used to it. Art of Illusion or Sketchup are simpler...

ok

PS I am curious as to how you use Inkscape for your 3D modelling. Sometimes it could be useful to start a model based on a 2D SVG sketch.