Is my interpretation of the circuit with N-Channel MOSFETs correct?
- When IN = 1, MIDDLE = 0 and OUT = 1?
- When IN = 0, MIDDLE = 1 and OUT = 0?
Your power supply is backwards. Other than that, you are correct at an abstract level, i.e. assuming the gate voltages get high enough on "1". Every stage you have there is a NMOS inverter:
IRF530 seems rated to work only at VGS above 4.5V, so in practice your circuit probably won't work with that 3.3V power supply (even if properly oriented).