To delete something, right-click on it and select Delete from the menu.
To rename something:
To resize something:
You can also adjust objects in the Viewport directly by toggling between the Manipulator buttons in the Toolbar and moving the axis.
Yes. You can change an object's properties so that, for example, it appears while the user is capturing the effect but does not appear in the final video or photo. To do this:
Both boxes can be checked at the same time.