Thanks for the details.
About reflection/refraction values: at this moment reflection is set to 4 and refraction to 16; do you mean I should reduce refraction to 8 for better results?

Unit conversion seems works fine but different converters have different fraction constant.

Not sure I understood. Maybe you meant that each metric unit use a different count of decimals? It's on purpose, because values smaller that millimeters are not shown, leading to one decimal for centimeter unit and 3 decimals for meter unit.

A button to clear cache(%AppData%\Roaming\eTeks\Sweet Home 3D\work) after complete project

That won't happen because temporary files that aren't necessary anymore when program runs, should be deleted automatically. After an inquiry in source code, I discovered that some temporary files needed for SunFlow rendering weren't deleted once the rendering engine had finished its job, and I fixed this in the Beta 7 that I just released. All other files in the work subfolder can't be deleted before the program ends.
The Beta 7 fixes also a bug that didn't show correctly rotated textures in SunFlow renderer (thanks Hans for reporting this issue).

If you are planning to change render engine then please sunflow as plugin& yafaray instead.

That's what I had in mind too, but as Yafaray isn't programmed in Java, it won't be easy.

Sorry, other wishes won't happen in the next version.