short depth 2U Plex NAS

[ed]

You could go for Synology RS1619xs+ and an expansion unit. Or bigger drives such as 20TB.
Either way, you need to look at Xeon CPU for remote streaming.
Local streaming does not require expensive hardware.
Maybe this depth table is useful https://nascompares.com/answer/short-dep...-nas-list/

I hope this helps.