Dont forget one mayor thing. Replication does not protect from data corruption. So... if you have (lets call primary NAS R1) R1 in RAID 0, if you loss disk, and in doing so you get data corruption (opened file, files in transition and similar) that data corruption will be replicated to all other NASs.
My recommendation is to have RAID5 or raid 1/0 on primary and then have RAID 0 on second NAS where you can use extra space for multiply copies or versioning (snapshots) and then again raid 5 on last NAS for long term security of data.