If you know that keeping Roos could potentially get yourself into trouble, the worse thing you can do is go out and get several. I'd start with just one, and see how it goes. When starting breeding projects, since those produce even more fowl, it's best to wait until you have a lawful place to experiment to your hearts content.
With multiple roos, they'll compete with each other. If one hen starts cackling, one Roo will start, then his buddies will start. And so on and so forth. My neighbors have 3 roos, I can indentify each crow now.
(which is why I want to start back into chickens, I hear all the dang noise and don't reap any of the benefits)
The dark box is a great idea, and it does work. When I had my last chickens, my dad would hear them start at 4am and it would drive him crazy. So we boarded up the mesh sides of the coop (was a converted rabbit hutch) and they quit starting so early.
Instead, there was still some ventilation... which the kitchen light would hit directly from a window when my dad did get up, and that would set them off. This time though, after the bread winner was awake and rested.
I would test the waters of your neighborhood with one Roo, and a dark box. If no one says anything for 6-7 months, then get a 2nd Roo.