It really comes down to what your budget is and what you plan to do with the Pi long term. If I recall correctly, the Nerves Livebook distribution booted up uses about 100mb of memory. So anything above the Raspberry Pi Zero 2 W (in terms of available memory) will be more than capable for what you throw at it for this book and future Nerves projects.
If you plan on using the Pi after this book for a lightweight desktop computer or media player, you may want to get the 8GB or 16GB Pi 5.
