Hi,
      Input Swing is usually limited by your Opamp Gain because that decided the difference in voltage/currents at two input nodes. On the other Hand, Input CM Range ICMR is defined by the range of voltages required to maintain all the MOSFET's in desired(usually saturation) region of operation.

While designing a unity gain buffer, You should primarily be concerned about ICMR because usually that's the one which will set the limit on your choice of output common mode level.

You can estimate ICMR by the values of overdrives that you set for your tail current source & load transistors. You can simulate it by sweeping i/p CM level and checking the limits for all MOSFETs to be in desired region of op.

happy to help,
Mayank.

Hi ,
     
      In an opamp, o/p analog gnd would mean the voltage level wrt which  you measure your o/p voltage.
      In an OTA, it would mean the VSS rail of the ouput branch i suppose, which is generally the same as reference voltage with respect to which you see the output.


--Mayank.