I just did this last week. I originally tried stalwart as that seemed to be a pretty small footprint (1 docker container) and had built-in PGP support. But I couldn’t get the built in acme bot to work with my dns provider, maybe you’ll have better luck.

I then tried mailcow and had e-mail flowing in under an hour. Of note, there are a lot of containers if you go the docker route, some may not be necessary if you just want email. I have so far left the default containers running as I don’t really care about the extra containers, it’s all running on a vm w 5 GB of RAM. I’m not concerned about PGP at this point as the server hard disk is encrypted via LUKs.

I can’t speak to your first 2 questions, dovecot comes with mailcow, but I didn’t have to set any specific settings for it.

I port forward directly to the vm, but it’s on it’s own isolated VLAN. use 993 for imap instead of 143, it requires SSL if using a proper mail server.

I use thunderbird for desktop and fairmail for android. I’ve not used

I hope this helps!