1) Comparable Chart between iClone and 3DXchange.

2) How can I see the opacity result in a 2D image?

Please switch to the pixel shadow mode.

3) I find there are more models shown when an skp file is opened in 3DXchange than in SketchUp, it seems that they are hidden in SketchUp.

Show layers in SketchUp then you can see these hidden objects.

4) The result is incorrect as I load a huge model (over 100,000 faces), what shall I do?

Please set the scale to 1 for a huge object and you can see the right result.

5) When I load a very big object, the bounding box disappears. What shall I do?

Please set the scale to 1 for a huge object, then you can see the bounding box.