Upload & Sell: Off
Help on the product selection or determining if you need more lights? It's based on what you are trying to do.
Though the B400 and EXD200 are not the most powerful lights, I still would not place them in the same decision making category as the YN560. The Yongnuo (and nearly any other hotshoe type flash) are great for portability, but are less powerful than the other two in you list. The Yongnuo is not exactly interchangeable with the others.
Even with the above said I would still suggest the YN560 based on what you have and where you are starting out. You can train yourself on proper lighting with your SB-25 and the two YN560s....though you can do the same with your current SB-25, a reflector, and proper placement of ambient light too.
There are TONS of options to consider but it all boils down to what, where, and how you plan to shoot. In other words, your interest.
This guy in this thread bought gear but he didn't know why nor how he was going to use it. Don't fall into that situation. Get an idea of what you want to shoot and use what you have to max it out first. Go from there. Don't purchase just because you see others with 2 and 3 lights. The sun is a light. A reflector can create light. Etc.