If you mean whether you can combine all sizes in all shapes with all covers and themes, we’re afraid you can’t do that. There are strict restrictions regarding which covers can be paired with which sizes, and which sizes can have all available themes. For instance, pocket sized books are often not available with certain covers, while the same could be true vice versa: bigger books cannot be ordered with “cheaper” covers.
Our only advice: before starting the editing process think about what you need, or, to be more precise, what you can/want to spend.