To create a character, you'll need a certain number of levels among all of your previous characters, added together. Your first character is free, but beyond that you'll need to do some fighting, as shown in the following table. Each column indicates the number of total levels needed to create another character.

Once any of your characters reach level 60, you may make another one to take his or her place, ignoring the normal character limits. This is the only way to get more than seven characters.