Great plan! We need more independently hosted email. I’ve been self hosting email for 20 years. Still running Postfix and Dovecot, but don’t have all the features you’d like though. I just wanted to chime in that I’ve moved from spamassassin to rspamd. And I’m happy about that. Given your experience in the hosting business I think you’ll like rspamd. One thing I have changed since a few months is have outgoing mail go through Amazon SES. I moved hosting from Linode to Hetzner and that turned out to be not so great for outbound delivery reputation. I didn’t want to migrate back to Linode so I bit the bullet and compromised with SES. That has been really working well, but I admit it is a bit of a step back from fully self hosting.
Great blog post, always nice to read about other people’s experiences. I was curious if you’d switch back to NixOS, but that’s not the case. Cubes OS looks interesting, I checked it out a few years ago. I should give it another look.