You state that you want to measure the medium (median or mean), minimum and maximum values of the mains voltage. I would point out that there is a difference between the mean and the RMS values of the voltage waveform. From your schematic I am guessing that you want the average, minimum and maximum values of the RMS value of the mains voltage. As you read my suggestion you will understand making the distinction.

My suggestion would be to use a stepdown transformer, but do not rectify the voltage. Instead measure the actual waveform with your ADC and do the calculations in your firmware. If you only need a single RMS value per second, you can calculate it. But, if you decide later to measure for something else (say peak voltages or frequency fluctuations or drifting above and below some reference ground) it will just be a firmware change. The same hardware will still do it. There really is no need, that I see at least, to change the representation of the voltage in hardware, except to step it down to a much lower value.

That's my two cents worth...