Isolated thermistor measurement
Thermistors are relatively high level devices and are not generally grounded so it's not usually necessary to isolate them. You can add a low pass filter and use shielded wire to the thermistor if you expect significant EMI. 

You should check the reverse leakage of those Schottky diodes- if they are the type I think I see-- at -4V and 75 degrees C they will typically leak 200uA! 



Edit: 







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