Good place to start on Special vdevs… Special VDEV (sVDEV) Planning, Sizing, and Considerations
To me, a metadata svdev makes sense for a media server since most files are large/very large.
Support for the nVidia P400 was dropped in TrueNAS 25.10 due to the change to the newer nvidia kernel module. The last TrueNAS version to support it is 25.04.