Hi @George ,
as promised here my tutorial:
https://forum.commonvisionblox.com/t/getting-started-displaying-multiple-cameras/1508
You will see, UI and Logic are much cleaner separated from each other up to the point where you can change the whole UI without changing anything in your logic and vice versa.
Also you dont need the whole Streamhandler and UI stuff.
Regarding your questions:
mainDisplay.ShowCursorPosition = true;
To show where on the display the mousecursor currently is
mainDisplay.SelectedArea2D = new Area2D(new Rect(10, 10, 100, 100));
To change the selected area.
Cheers
Chris