Saturation of air within isolated system with water and ethanol

I am planning an experiment in an isolated system that contains two droplets.
One droplet is water and the other one is a 40% ethanol-water mixture.
The isolated compartment is filled with air at 20°C.


I understand that for ensuring that the water droplet volume remains constant during the course of the experiment, the air in the compartment needs to be fully saturated according to the vapor pressure of water at 20°C (100% relative humidity).


Under these conditions, my understanding is that the ethanol from the 40% ethanol-water droplet is not yet in equilibrium with respect to the evaporation/condensation rate in the fully water-saturated air, thus decreasing the droplet volume. Is that correct?
If it is correct, that would mean that I would also have to saturate the air with ethanol before the experiment. I can find the vapor pressure of ethanol for 20°C. But how would I calculate the resulting concentration of ethanol in the air in kg/m^3 or ppm?
Also, how would the total air pressure within the compartment be influenced by the saturation?


