that's a somewhat expensive setup to still do all the work of dealing with dead drives and manually doing replication and dealing with conflicts (I fear the pain of dealing with his 4way daily backup of the same data over desktop/laptop/2 pen drives)

zfs rent = 4+TB drive + $10/mo (base 1TB) + $5*3 (extra 3TB) = drive + $25/mo

hetzner = 5TB $10.9/mo

vultr = $5/mo (probably more)

4x ~4TB drives = $800

assuming you replace drives every 5yrs: $3,254 or $54.23/mo.

assuming the drives last 10yr which are common now: $5,708 or $47.56/mo.