Has to do with lowest stress and quickest resilver.
Could use 3 bay RAIDZ1 with hot spare, but that is more stressful on all drives.

My plan A.

System 1: The back end. (Lower performance CPU). A 4 bay terramaster F4-424 pro should use 2 mirrors in raid 10 format.

System 2: The front end.

A 6 bay terramaster F6-424 MAX (higher performance a bandwidth:
Should use 2 mirrors or if 2 extra drives are added use 3 mirrors, all in RAID-10 format.
Have a cold spare available. Back up system 2 to system 1. Back up both to external USB drives and rotate offsite. 1 to back, 1 to cloud.

Have a third system in another location for fault tolerance.