How do I install zfs on manjaro post-install? Just to create a pool across drives that are not to be used as root/boot.
if you have both a GPT AND the AUR activated, you just need to:
pamac install zfs-linux
and then start creating your partitions…
As you mentioned: root on ZFS is the difficult bit, so no issue in your use case.
P.S. Please note that’s a big if!