2. Do they have to be different of the same? (if the same, they're going to be on both sides, kind of like right now but more realistic)
Can be different, up to you.
3. Do you want assassin looking images or more of a suit like or even a robotic kind? (if you want them to be more realistic, I guess robotic images are out of the question, but it is still an option)
Preferably assassin-looking. Robots should not be included.
4. I was thinking something like a Ninja on one side and a special agent on the right side, but came up with this instead. I still have images ready for the assassin/agent version. So, will Ninja/Agent be something you are interested in?
Yes, if you can make it look good, why not. Put the ninja on the "traditional side" and the agent on the "future/city" side.
5. Just overall write something out of your head so I can draw a mental scetch of your vision in my head. That would help me with a design.
I like your idea. Just make sure the ninja/assassin guy isn't exaggerated. As in, having too many anime-like traits or posses ridiculous weapons/symbols that don't really fit with what I would call a "realistic ninja". Someone who wears dark clothes, perhaps a hood and a mask, with a realistic weapon that fits with the theme is what I'm looking for.