The nozzle does not atomize the water, and it doesn't need to either. When the water is injected into the carb it will atomize as much as it needs to as it's pulled through the intake and into the cylinder. Don't get hung up on worrying about atomization.
The pickup tube sits in a "jug" that's similar to a winshield washer jug, and works the same way. It's vented and the tube sits near the bottom so it picks up water when the system calls for it.
If you make your own system you'll need some sort of brain that tells the system to pump when the vacuum drops below a set inch of vacuum amount. If you build a system that works off throttle position it wont ever come on until you press the throttle hard enough to call for it. A lot of detonation can and will occur before you ever reach full throttle.
You don't need two vacuum sources. You want the system to work regardless of whether you're on the highway, or around town. I doubt it would ever come on while cruising at speed, as that is when vacuum is at it's peak and there wont be detonation just holding a steady speed.