For the average home NAS, Read/Write performance is not usually a critical factor.
Space efficiency is often the main reason why people with 3 or more drives decide to use something other than RAID 1 (mirroring). But, IMHO for the average – less technical – home user, anything more than RAID1 is asking for trouble.
The biggest benefit of RAID1 is simplicity. One drive mirrors the other. 4 x 4TB drives = 2 x 4TB storage in 2 x 4TB RAID 1 mirrors.
If a drive fails, replace it and the mirror will rebuild. Do it ASAP because you want the rebuild to happen before the sole remaining drive can fail.
If you want to treat the array as 1 x 8TB device instead of 2 x 4TB, you can look at RAID10 which benefits from RAID1 and stripes the two RAID1 arrays into a single device.
However, I would again suggest KISS. One of the biggest risks with a home NAS is that when a problem finally occurs, it has been AGES since you built the thing, and you don’t remember the config exactly – what goes where, what to do to rebuild etc.
RAID1 RAID10 4TB | 4TB 8TB RAID1 | RAID1 RAID1 RAID1 (4TB) | (4TB) (4TB) (4TB) (4TB) | (4TB) (4TB) (4TB)