I use zfs everywhere, even my 4GB RAM PI4 is running zfs. It provides better data integrity due to checksumming. Even without ECC it’s a (imho) superior filesystem because RAM bit flips aren’t that common. (And once data is written to disk, it won’t get modified, unless you have access time still enabled)
Also the cache is nice with zfs but only really helpful for storj databases. So if you move your databases to your ssd, it makes not much sense to have a slog/l2arc for your storj HDDs.
You can read a bit about zfs cache and recordsizes here: Best Record size for zfs