Also, I am confused at why nextcloud is at the intersection of networking, music, and multimedia.
Yes it technically has a video viewer and music player, but I would be very surprised if any person in the world right now is genuinely using it to post that content to the fediverse social-network style.
This is a good way to do it.
I went one smaller with the Node 304 which only can do 4 HDDs with a GPU inserted. Going used for consumer desktop CPU is the most powerful play for the money I think.
This is a good path forward OP for a pretty powerful server