@Hyolobrika
I don't have experience hosting public e-mail services, I'm only considering migrating off Proton myself, but if you're interested, DeltaChat has made this set of scripts: https://github.com/deltachat/chatmail
As you know, the underlying infra for DeltaChat is email, so they are basically deploying dovecot and postfix — you might use this as a source of hints on what software to use or maybe even use it as is.
@Hyolobrika
I'd use this myself, but their scripts seem to rely on systemd and if I go for a VPS, it'd probably be a BSD of some sort or Alpine, so I probably would have to make some of these things manually in order to make it work.