Rainer,

Q1 and Q2 depend on the hardware of your computer, especially the 3D capabilities of your video card and driver.
Q3 and Q4 are hardware-independent; they use the SH3D software, including Sunflow for rendering.

The installed version comes with its own Java. That's the version I always use. You could try the webstart version and/or the online version to see if there is a difference.
For more technical info, ask Puybaret.

And, no, I didn't have anything specific in mind when referring to the FAQ. Just hoping that one of the suggestions there might be helpful.

H