I tend to assume that ECC RAMis well standardised and generally better quality than average. For extra peace of mind, go directly for first-party manufacturers: Micron, Samsung, SK Hynix.
Mirrors: 2
Raidz1: 3
Raidz2: 4
copies=2: 1!
Add at least one drive (and possibly a few more) for a backup elsewhere to keep your data safe. ZFS can have hiccups. Burglars break in. Houses burn or get flooded. Sh!t happens.