I feel like the warning pretty much defeats the purpose of RAID-Z1
The real way to look at RAIDZ1 is that it protects you from bitrot/UREs, but not from drive failure. Obviously, that's more of a statistical argument than a hard-and-fast rule, since RAIDZ1
would protect you from drive failure only if you had
zero bitrot/UREs during rebuild. However, it's a pretty good rule of thumb to treat RAIDZ1 protection from data damage only.
I'm not too worried about wordpress though. Yeah it can be exploited but I'm not too sure how worried I am about that if I keep it regularly updated. It seems a lot of the exploits I see are because admins are using old versions of Wordpress and that's what gets hit. I'm open to alternative ideas for website software though.
If you host a website or email in your organization's network, you
really should put it in a DMZ of some kind. No matter how good you are as an admin, and how quickly you update Wordpress, zero-day threats are a fact of life, and it will only be a matter of time before your website is exploited. If your website is on a DMZ, then your data (and your network at large) will still be protected. If you mix it in with everything else, then your risks are
much greater that serious (e.g. ransomwear) damage could be done.
Same thing also applies to Nextcloud. Or, a better way to use Nextcloud might be to set up a VPN, so you're not directly sharing it with the outside world.
Would 32GBRAM honestly be necessary for Nextcloud and Bacula though?
It's really more a function of your use case. ZFS loves RAM, and if you have multiple simultaneous users, you'll benefit from the additional memory. Nextcloud probably won't be that memory intensive on its own (though, depending on how many files you share, its database could get pretty sizeable, pretty quickly), though Bacula could indirectly need more memory because of the additional strain on the array. I would personally consider 16GB to be a bare minimum for just file sharing in any enterprise (even small business) environment, and with the additional load of the jails, I would jump to 32GB.
At the very least, if you
really don't want to spend the money now, you could always see what your performance is with 16GB, and then get another 16GB if and when you need it.