I think you already know why its a bad idea to release previously captive box turtles into the wild, since that territory has been covered many times before in several different venues.
I know that you have a tendency to ask questions for which you already know the answer: you may want to find a better way of framing your questions.
Rehabbers typically have been well trained and are licensed, and have the means to do a much more thorough health check than yourself, which is why they can re-release rehabilitated animals, and you should not.
As for your new pen: I would keep as few as possible in a pen that size. You've run into problems in the past with not having funds for proper care, and the situation getting out of control. I sincerely hope you've learned from past mistakes, and will keep as few as you can realistically manage at one time.