z stack of Display Boxes?

[#1]

Can I place display boxes on top of ach other?
e.g. the Icon box at the top left corner, inside the picture box?

Names Default To Here( 1 );
New Window( "Example",
icon Box ("Error"),
	Picture Box( Open( "$SAMPLE_IMAGES/windmap.png", png ) )
);

[#2]

You are able to sometimes overlay some displayboxes on top of each other using margin/padding but I'm not sure if that is possible anymore. With just PictureBox you could most likely just plot the icon in the same picture?

[#3]

Barely. Not really supported. But What is an Alpha Channel?  has an example of exactly this.