If i understand well, if i put a bandpass filter at 50Hz, this interference will not be amplified by the amplifier, so it should not saturate the amplifier, right?
I put X2 to get a x100 gain, avoiding the use of a 1GOhm resistor (is it a good idea?) and X3 to have a current boost to be able to read larger current when i change the feedback resistor to a smaller values.