Potentially supporting datapoint: I've found issues with netbsd-9 with ZFS on 4GB. Memory pressure was incredibly high and the system went away every few months.
Currently running fine on -9 & -10 machines with between 8GB and 192GB The three 8GB ZFS machines (netbsd-9+raidz1, netbsd-10+raidz0, netbsd-10+raidz1 Frankenstein with a 8TB and two pairs of 6TB & 2TB) all seem to run fine, but they only have around 24TB of ZFS storage David
