Hello,
you can find information here:
http://calgary.rasc.ca/field_rotation.htm#vary
DeepSkyStacker easily manages the field rotation between the successive frames as long as you use FireCapture with the dark subtraction (for DSS avoids confusion between hot pixels and real stars). But no software can manage the field rotation during acquisition.
The best way is an EQ mount.
I don't know what is the real acceptable maximal exposure with an ASI120MC (I have a ASI120MM: 5-20 seconds are fine. Perhaps much longer is feasible if the dark frames are correct with respect to the variation of ambiant temperature). The "slow" mode in FC (if available in colour version) may help to reduce noise.
Nicolas
