When choosing outdoor lighting it is not always necessary to have the same style throughout although that is okay too. Choosing two different compatible styles can be interesting. Each side of the building could have the same style fixture although in different sizes: (ie. larger on the garage than by the patio doors. Or the courtyard could have a different style than the front door.)
The size of each fixture is dependent on the area of installation. 8” wide fixtures look better next to standard height doors. 10” wide fixtures or larger look impressive when hung next to larger doors or on large walls.
To approximate the correct size ,make a rough mock-up of the fixtures you are interested in using cardboard, string and tape is a great way to approximate the 3-D fixture in place. All measurements are listed in the catalog for each fixture. Start with the biggest size you are considering. It is easier to cut down your mock-up from a bigger to a smaller size.