And you can get “new” from AliExpress around 80-90€

Same here, I’m too paranoid and checking access logs and attempts made me to stop keeping any other port open than wireguard.

Self hosting mail server is one of the worst ideas. You need to have top notch security, always updating patches and on top of that somehow manage to get your mail not to go into spam folder. Google and Microsoft don’t usually like self hosted emails.

If you still are going to go through with this, good luck! I’m going to check regularly how your path goes. Sadly I can’t help you at all, just some wide words repeated by others.

Debian is excellent choice.

Or do Sony and make it Xbox one II