1. Screens are displayed into layouts, so you can use a layout to display one o more "screens", or use different layouts for different screens. It depends your design. In example, a layout sheet can create and destroy objects and/or show different menus on different cases.
2. Game is paused on windows focusout event but you can handle the pause events by yourself. Please search in forums, it's plenty of info about that.
3. A layout starts each time it's invoked, maybe you want a persistent layout, check then the Persist behavior.