I killed myself, did I win?
I don't know of any official rulings on the game, but I would not interpret that as a win for Charles.

The sticking point is:


  At the time you kill another character, the total number of dead characters is 3 or more.


So what was the total number of dead characters when you killed the Hunter? Your interpretation is that it was 3, because a Shadow was dead, the Hunter was dead, and Charles was dead. 

However, I don't think this works - at the time you killed the Hunter, Charles must have been alive; dead characters can't attack, after all. Thus, Charles would have died after killing the Hunter, which means that at the time you killed the Hunter the total number of dead characters was 2. 

Fundamentally, the reason why this situation is confusing is because Charles should not have been able to attack at all. I'm not sure if it's an official rule (I'll check later), but a lot of other game mechanics assume that if you reach maximum damage at any point during your turn, your turn ends and your character is dead - for instance, if you have two health remaining and draw the Spider card, you're dead and your turn ends, you don't get to attack.

Since Charles' ability deals two damage to him first, and then allows him to attack, by triggering your ability you should have simply died without doing anything.

As for the last part of your question, I think there is no way for Charles to be the sole winner in a five player game. As soon as three people who aren't him are dead, the game is over; thus, he either wins a joint victory alongside the Shadows or the Hunters (by taking the last kill), or he doesn't win.