In cmrf8sf GIDL won't be a problem.
As of the second point, the current through M1 will go up or down depending on how you move it back into saturation:
- if you resize M1, moving it back into saturation means the voltage on top of the 3 diode connected NFETs went down hence the branch current went down
- if you resize or change the NFET diodes keeping M1 the same then you are right since you operate at constant Vg you just follow the Vds vs Id chracteristic