I do not have the PC version of Oblivion, I will be getting it hopefully today. But I do have the PS3 version.
I have watched my friend play the PC version, and I see that the Save Screen is quite similar to the PS3 version. My little brother and I will be playing on the same copy. So there will be at least two different characters. I was wondering is the a way to change that through mods, such as having character slots - to organizer your characters.

So is there a mod for Character Organization?

Wrye Bash has a save organization function among the tons of things it does.

You should really read up http://tesivpositive.animolious.com/?page=intro_to_mods to get your modding basics in place before you attempt to play modded Oblivion... Wrye Bash might seem insurmountable and too complex at the beginning, but it is the one tool that will help you the most to have a more or less crash free experience.