

Yes. You can just get by with 2 devices but you need to set expected_votes=1 in the cluster config somewhere, don’t recall where, and I’ve encountered issues with stability with that solution, seems like it’ll get undone though I haven’t used it for years to say if that’s still the case.
The q-device will work on anything Linux that’s available when the second node is down. Not having the tie-breaker isn’t the end of the world, it just means you have to go in after you bring up the second node and start some things manually, and if you’re replacing nodes in a 2-node cluster, it’s much nicer to have the q-device.
It’s not Nix-specific, but I use Mailcow-dockerized and it is completely hassle-free, been using it for 4 or 5 years now without a bobble (though I’ve run my own mailserver for 30 years).
I would agree that a static IP is necessary, but I don’t have one and I get by, even without a PTR record. That’s probably due to a fairly small ISP with not many spammers having found it.
Make sure you set up your DKIM and DMARC right from the start and pay heed to the reports. But I’ve never had to fight to get off a blacklist, even with new domains I’ve added to it.