Consistency has been a part of each and every rule thus far, but it's important enough that I wanted to emphasize it one last time. The power of consistency is that it makes your readers comfortable; they know what to expect in the formatting so it fades into the background and they can focus their attention on the content of your outline. If you make an error but make it consistently, sometimes your reader won't even notice! It's when you start changing things constantly that you call attention to how you are writing instead of what you are writing and you divide your reader's attention.
A Note About Formatting: Outlines usually follow a specific format using parallelism, Roman Numerals, upper case letters, and sometimes numbers to indicate ideas with different levels of importance. Unless your instructor is planning to collect and grade your outline based on proper formatting, try not to get too hung up on making sure that you're formatting each section properly. The important thing to remember is that the outline is meant to be a helpful organizational tool --compose your outline in such a way that it will be helpful to you !