That's the weird part. It's trivially simple to run a Minecraft server. Slap whatever your favorite variant of Linux is, install Java, run minecraft-server.jar. Make a service for it (heck I made one many years ago, probably still works: https://gist.github.com/chungy/0b2c438c7db90b32701a).

Once you have the Raspberry Pis, pre-installing an operating system to run the standard Minecraft server should be the easy part.

Unless, of course, it really was a case of "reverse engineer and reimplement Minecraft to make my own server." Not strictly impossible, but a completely unreasonable goal.

> Unless, of course, it really was a case of "reverse engineer and reimplement Minecraft to make my own server." Not strictly impossible, but a completely unreasonable goal.

Hasn't that already been done several times? There's feather-rs (fairly mature but reduced set of features) and Pumpkin and FerrumC. And, for that matter, Paper - that one is Java and I haven't checked to what degree it's just borrowing from the original implementation, but I do know that Paper is actually used for real servers.