Is this small-signal gain correct?
This is common source amplifier for which the gain is given by \$-g_{1} * Resistance_{seen by the small signal VCCS }\$
The small signal resistance seen by the small signal VCVS of \$M_{1}\$ is \$r_{o1}||r_{o2}||r_{o3}||\frac{1}{g_{3}}\$So the small signal gain of the system is \$-g_{1}(r_{o1}||r_{o2}||r_{o3}||\frac{1}{g_{3}})\$And for sanity check \$r_{o1}=r_{o2}=r_{o3}=infinity\$ the gain is equal to \$\frac{-g_{1}}{g_{3}}\$