There is no formal character limit on Lights Out. However, it is asked that you be smart. Don't create a million characters and then not use them. Only create what you will use.
When you are going to create a new character, you will create a new account for them. Each character you have will have their own account. If you'd like, you can choose one account as your "main", and anything off-topic will be done there. It is asked that you do so for purposes of being less confusing.