Instead of 4 x 6TB drives, consider 2 x 14TB or even 2 x 20TB in a ZFS mirror. Buy the biggest drives you can afford that have reasonable pricing. When I was buying drives two years ago, 16 - 20GB was the sweet spot for price per GB.
Make sure you use NAS drives. Western Digital has had several controversies so I usually go for Seagate Exos instead.
I’m the same as you - I had experience with mdadm, LVM, LUKS, and ext4, but no experience with ZFS. I still don’t know a lot about ZFS, but Unraid set it up for me, and I can always Googl4/DuckDuckGo any issues I encounter.
The thing is that it’s likely that lots of people are affected by bitrot and just don’t know it, since there’s no way to detect it without using checksums. People don’t know that their files have succumbed to bitrot until they try to use them and realise they’re corrupted.