As to the humidity question, I don't believe their is an exact universal right answer due to variables that need to be taken into consideration: Altitude and Relative Humidity in the air where you live.
I live in SE Louisiana and am only 84 feet above sea level: I mostly use dry incubation until lock-down. Last week, our relative humidity outside was 94% and even with the central air on inside the house my incubators (a brinsea octagon advance 20 and a little giant with fan) both maintained between 34-50% humidity with no water added.
From what I understand, air at lower altitudes has more oxygen and water molecules per square foot than at higher altitudes. This affects the heat transfer ability of the air in the incubator. After that it gets technical, but the gist is that one shoes won't fit all, although it will fit quite a few applications.
Follow this link for some interesting information about the affects of altitude on incubation. All measurements are in metric, but are based on 100 degree F temperature constant for the embryo.