If you are not going to be using ZFS — then there is no point in true nas scale (leaving it’s readiness and stability compared to core aside for now).
I would go with fedora/rhel/Oracle Linux, definitely not Ubuntu.
I would further recommend podman in place of docker.
And even further — run nodes directly. On a resource constrained system there is no reason to waste them for OS virtualization.
But on the other hand, I would consider going with TrueNAS Core, single ZFS pool, with special devices for metadata using fast SSDs, and running storagenodes in jails.
That is if you want ultimate performance, scalability, and what’s more important, stability. But you need to have at least 16GB of ram, and the more - the better. (fastopen is not yet enabled for FreeBSD nodes, but I don’t think it’s such a big issue; it’s a small trade off for stability and resilience of FreeBSD and ZFS; ultimately I hope storj will enable it for this os as well Please enable TCP fastopen on your storage nodes - #8 by jtolio)