Yeah, I leave the top vent open the whole time. I feel like the extra air is just better.
For chicken eggs, I agree 50% sounds high. But if the air cells look good it's probably fine. Humidity needs vary based on location and elevation.
Like Andrea said, you can run it just fine without water. I wouldn't recommend doing a dry hatch in it, but a test run is ok.
Though to do a test run you usually want to mimick the settings you'll have it on during the incubation period, so it's good to test it with water in it.