I was about to suggest the same: Proxmox VE on the m710q, and something like TrueNAS, or good ol’ Debian (using NFS so the m710q VMs can mount remote folders) and podman/docker/whatever on the i5-4590 to run stuff like Jellyfin.

Another possibility: Proxmox on both, clustered (not that really hard to achieve), with a “NAS” VM on the i5-4590 node and another transcoding/media-player VM with Jellyfin (you can relatively easily expose PCIe stuff to a VM with Proxmox nowadays, including a gfx card).

If OP prefers runing LXC containers, Incus can also be an interesting choice.