Zfs doesn't need hugely resourced hardware. For example, it can run on a single disk and still get you cheap snapshots/rollback, on-disk checksums, potential for easy replication via send/recv, highly efficient caching via the ARC, and transparent compression amongst other things. You can also start with a single disk and then easily add a mirror later on.
In terms of CPU and RAM, most NASs now are perfectly capable of running it (but do also consider speccing out a small form factor PC with a case with lots of drive bays vs prebuilt NAS - you might be surprised at what you can get for a similar cost).
In terms of CPU and RAM, most NASs now are perfectly capable of running it (but do also consider speccing out a small form factor PC with a case with lots of drive bays vs prebuilt NAS - you might be surprised at what you can get for a similar cost).