I run my Truenas Scale with 5 mirror vdevs. This is sort of like raid 10 (I don’t need the differences explained to me). This means that I get 50% of the raw storage as usable but, it means that to upgrade space, I only need to upgrade two drives at a time. It also means that replacing a failed drive is fast, much faster than replacing a drive from a raidz* vdev. As you move to Truenas, this is something to consider. Given that you’re going to have 4 drives total, I don’t think you’d be wasting any additional space as you shouldn’t consider raidz safe (same problem as raid 5, high risk of second drive failure during rebuild) which leaves you at raidz2.