1GB RAM per 1TB storage is really only required if you enable deduplication, which rarely makes sense.

Otherwise, the only benefit more RAM gets you is better performance. But it's not like ZFS performs terribly with little RAM. It's just going to more closely reflect raw disk speed, similar to other filesystems that don't do much caching.

I've run ZFS on almost all my machines for years, some with only 512MiB of RAM. It's always been rock-solid. Is more RAM better? Sure. But it's absolutely not required. Don't choose a different file system just because you think it'll perform better with little RAM. It probably won't, except under very extreme circumstances.