
Explanation:
Box 1: No
You can reorder screens.
In the left navigation bar, hover over a screen that you want to move up or down, select the ellipsis button that appears, and then select Move up or Move down.
Graphical user interface, application Description automatically generated

Box 2: No
You can add screens to the app after it has been created.
Box 3: No
For example, you can change a button's shape. By default, Power Apps creates a rectangular Button control with rounded corners. You can make basic modifications to the shape of a Button control by setting its Height, Width, and Radius properties.
Reference:
https://docs.microsoft.com/en-us/powerapps/maker/canvas-apps/add-screen-context-variables
https://docs.microsoft.com/en-us/powerapps/maker/canvas-apps/controls/control-button