I have been using the KiCad suite successfully thus far. Good stuff!
Yesterday I have pressed some key combo by mistake and ended up with this white circle-crosshair in the image below. Zooming in or out does not change its absolute size on the screen. What is it and how does it influence things ? Maybe get rid of it too
It’s the Grid Origin. It defines where the drawing grid starts so that one horizontal and one vertical grid lines cross at that point and others are positioned relative to that (for example in 1mm grid +1mm, +2mm etc.).
Open the View->Grid Settings dialog to reset that.
No. It’s possible to use “Auxiliary axis origin” as an option (see the plotting dialog) but that’s not Grid origin.
Grid origin can be changed according to your needs when drawing and laying out the board but don’t use it unless you know what you’re doing. It may lead to aligning problems of items if you change both the origin and grid pitch.