Over voltage and reverse polarity protection
A diode reverse voltage protection in a 5 volt circuit is not ideal. Even if you use a good Schottky you are still going to loose ~ 0.5V and the reverse current in some schottky's may still damage your circuit.
Overvoltage protection with a Zener is also not ideal. You need some margin so you must use a 5,6V zener, if not it will conduct &quot;nominally&quot;. A voltage at 5.6V may exceed your ratings. (And you need a fuse  - if not the zener will overheat and blow up)
What you want is an efuse. As your voltage is similar to USB there are many types, so I am sure you can find one that fits your need. One example is NIS6150. Your biggest challenge might actually be to find one that is solderable by hand. Most of these components are tiny.