Basic protection: what you need depends on how you see the product being used. For example 12V in an automotive use case is more like 13.8-14.5V while the engine is running. This affects your choice of TVS protection diode which must not begin conducting until above this point. Automotive also includes the possibility of load dump events (when the battery being charged is momentarily disconnected and the alternator inductance will cause the alternator output voltage to peak between at 60-100V), which if they occur frequently will cause a significant rise in the temperature of the TVS diode.
Fuses come in various forms, the simple wire fuse is a common solution, but needs to be easily replaceable. It also may allow short term currents that are very high, this makes choosing the best current value a more complex task than you might expect. There are other versions based on positive temperature coefficient resistors (look up the “polyswitch” made by Raychem and others). These effectively limit the current rather than make a complete break in the circuit, but it effectively means it never disconnects from the source.
Reverse polarity is simplest to do with a diode. A Schotkky diode will lower the forward conduction losses and be fast acting. The MOSFET solution is better still, but most MOSFETs will not accept Vgs voltages greater than 20V, so if the reverse voltage could be momentarily higher than this, make sure you protected the gate.
Are all of these forms of protection necessary? It depends on the use case.
If there is the possibility of having higher voltages present on the DC input, even if just for a short time, give some consideration to the input capacitor voltage rating which might benefit from replacement with a part with a higher rating.
The ripple current of both the input and output capacitors is also important because the rise in the inductor current comes from the capacitors, not the external supply for the time that the switch in the regulator is on. So if the rise in the current through the inductor is from say 2A to 3A, so a rise of 1A, then the input capacitors ripple current must be higher than this, and likewise the output capacitor’s ripple current, as it needs to receive this.
You haven’t mentioned EMC/EMI concerns, but at schematic level the most important addition is a ceramic capacitor in parallel with C33 (i.e. closest to U2) and another in parallel with C38 which must also be very close to U2. If you get this right, there is a fair chance that things like common-mode chokes on the input from the power jack may be unnecessary.
It is likely that you will find the present circuit is physically rather big. If this turns out to be a problem, many newer devices are available that switch at higher frequencies and so allow smaller magnetics and smaller capacitors.
