amateur option but...
I'm a complete amateur but the way I understood it is that the chance of disk failing is not the issue. It is the chance the multiple failures will occur within the rebuild window for the FS in play.
RAID 5 has one failure allowed, hence if you are using a 4TB drive that takes (I have no idea, 24h? someone?) then a second failure will result in data loss.
RAID6 is better since you can have multiple failures but I the recovery time would eventually become a problem depending on drive size.
It would be interesting to here the prevailing advice for HomeNAS of say 16TB or so, the configurations that make sense? It would seem RAID1 and RAID6 are the only "safe" ones.
Oh and a tape backup....!