1) PushButtons, CheckBoxes & RadioButtons are everywhere. Look at the File Explorer Options menu for example.
2) I know I've seen the CommandLink buttons but I don't remember where.
3) At around 9:40 in this video I explain GroupBox:
https://www.vistastylebuilder.com/forum/index.php?topic=1268.04) Copy Close & Pause are in the upper right of the Copy window.
5) The rest aren't used as far as I know.