I have no idea how to explain this any more clear....
let me try caps..
Not necessary. From your response it seems you're still missing the point, but I'm not sure how else to explain it.
SINGLE PLAYER = One person, You..the One running the game.. Makes BOTH of the characters. Only one person in character creation.. just ONE not TWO.
..except you can still invite another player to your game, despite choosing singleplayer at the "New Game" prompt.
MULTIPLAYER = Host and FRIEND in character creation. Each one making their OWN character. Two people in character creation....
..except you can continue to play singleplayer, despite choosing multiplayer at the "New Game" prompt.
The mode you choose when you create a new game *does not matter*. All it does is alter your current multiplayer setting in the Options > Multiplayer menu, which you can then turn around and alter again regardless of the game mode you chose when creating a new game. It is not a permanent choice, but to a new player (and I guess you?) it certainly seems like it might be one. Which.. is not a great thing.
At this point, if you don't get it, you don't get it. (shrug)