Copyright & Characters

I did some digging into this subject, and I'd like to make sure I understand the process clearly.

When it comes to claiming the rights to a fictional character, it must be in a piece of work (story, comic, art). Only then can it be submitted to the US Copyright Office.

When a piece of work is also published online, it is considered Intellectual Property by the creator at the time of publication. From what I understand, this is kind of a broad way to say, "Without going into too much detail, it's yours, but you're on your own for fighting for it".

By claiming actual copyright over the piece that the character is featured in, only then can legal action be taken.

I've also seen a few posts that recommend making a character "bible" to demonstrate how the character is unique in both creation and within the piece of work. Is this piece something that is recommended to be copyrighted as well?

FWIW, I've gone ahead with the pieces of work featuring the character's name, physical description, actions, story, and dialogue.

Is there anything I am missing? Or what other actions are recommended to be taken to protect these works?