In the past I've seen issues on sites of a character limit. It's no secret to anyone who knows me that I don't gel very well with them, but I understand the necessity for them.
When you create your account on Sentinels, you will be given 2 character slots. These can be used to create heroes or villains, whichever you prefer. You can only have a character created so long as you have an open slot for them.
Afterward, you will be given one extra character slot per every 50 posts that you lovingly craft for our forum until you eventually hit the cap of 6 characters. There may be tweaks to this rule down the line, but for now there are no exceptions. You are free to create and drop characters as you go, but do try and find something that sticks.