Complex circuit analysis
The ideal opamp model can be used to calculate the gain. 

Rin is ideally infinite, as the gate resistance of the MOS transistors are also infinite. 

The gain can be calculated by finding the current thorugh the  BJT at the output, and the output will be simply equal to this current times R5. THis current is also equal to [Vout(output of the inverter) - Vss ] / R3.

The output resistance is simply equal to R5||ric , where ric is the resistance seen from the collector of the bjt, you can have a look at the calculation of it in this document http://users.ece.gatech.edu/mleach/ece3050/notes/bjt/BJTBasics.pdf

What I don't understand is, why this circuit have different values for the supply voltages, i.e. VDD, VSS, or the ground symbol.. Therefore, I didn't calculate the currents, and I am not sure about the base voltage of the bjt.