Security from what? Get a threat model.

A NAT will restrict connections from the internet, but won’t stop attacks from your local network. As your network grows, it might be a good idea to isolate shitty IOT devices (firmware is often full of holes), home internet and sensitive devices like cameras.

Oh so that’s why you can’t buy them anymore, people are using them as microcontrollers.

For alerts I just have the server directly send email over SMTP to my address, no service needed. You could implement DKIM with such a setup if you wanted to.

Considering how overloaded lemmy.world is right now, a pi in someone’s basement would be better, and besides, centralization is bad. Federation is what prevents lemmy from becoming the next Twitter.