Moose, allow 2 characters if used as a tag team. If someone wants to add a character they have 3 choices.
1) Drop the existing one, if just to a managerial/coach role. 2) Put the original in a tag team with the new one allowing him to play the new character while not having to ditch the old one. 3) Just stick with the old one.
A simple rule. 1 singles or 1 tag team allows for people to play 2 wrestlers if they want. I assume your fed allows tags to work singles and even win singles titles in the right situation but the team would exist primarily as a tag team. And YOU can control it. So if Dev makes a 2nd character and that character starts moving towards a singles title then YOU as booker can choose to refuse to book him in singles matches OR stop booking Darling in separate singles programs. You can make sure no one has 2 singles running separate programs as booker while giving them as much leeway as you deem fit, and pull back if you think it becomes bad for the fed.
At least that's what I always assumed was the logical way OOWF should be ever since I gleamed no one is allowed to have a tag team on their own.
Or don't do either. If you can't find an image you like at either than don't force it. Just give me something you like and which will look good on the board.