Low entropy transfer function, output impedance
To get \$Z_{out}\$, simply short the input source \$V_1\$ and you end-up having three elements in parallel: \$L_1\$ and its series resistance, your load (which is a fixed value at the considered operating point) and capacitor \$C_2\$ with its ESR. Determine the time constants for the denominator \$D(s)\$ then the zeros for the numerator \$N(s)\$. The dc gain \$R_0\$ is \$R_3||r_L\$. For more details, please check my APEC 2016 seminar on FACTs (slide 90) where I detail the procedure.