I have not tried it, but would a 3D modeling program like Blender not be better for creating furniture?
Any 3D modelling program that can export to one of the formats supported for import in SH3D is fine. However there's a huge difference in learning curve between the different programs. Blender has long and very steep learning curve where assembling basic shapes in SH3D is simplicity itself. It's what you know or are willing to learn.So the distance that the arrow keys move things by depends on the zoom level... is the 0.1 cm limit because you can only zoom in so far? It's hard-coded in the getMinimumScale() method. Um... if it helps you, I could make you a build with that limit removed.
No need for a special build. The advanced edit plugin partly goes around that limit and I suspect that one of the future releases of SH3D will increase zoomlevels and hopefully precision. A good trick is to build furniture in scale 10:1 and after export divide by 10 when importing. The 0.1 limit suddenly is 0.01 using that trick. And if that is not enough there's other programs that can. I use Blender for a few tasks that can't be done in SH3D like bisecting or smooting. I've become quite proficient in editing obj and mtl files too 
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