Welcome to the forum!
Get a rack shelf and an odroid h4+ or h4 ultra with the 4x ssd (type-3) case. There’s also the option to get the smallest case (type-1) and slap the ssds in a 3x 5.25" bay to 4x 3.5" bay (or better yet, a 1x 5.25" to 4x 2.5" bay - the CMR-425 is nice) from Chieftec (they’re more available in Europe, so go for them if you can), IcyDock or IStarUSA.
Alternatively, get a 1U or 2U case (rosewill make some good 2U cases, idk about 1U) and get a board with an intel n100, n97 or i3 n305, with a pico-PSU and 4 SSDs.
Slap proxmox on it and make a zfs pool for exporting SMB and NFS.
Try moving to Jellyfin if you can.
Time to learn to Netboot your Pi to run root-on-nfs on a zfs ssd pool (assuming your pi is wired).
Alternatively, install Alpine on your SD card. The default alpine pi install is the diskless mode, which means alpine will run from RAM. Workable on the 4GB+ versions (maybe even the 2GB model), but terrible for the 1GB model. The 1GB model will probably work with pi-hole though, if you disable logging. Octoprint might also work on alpine, but idk the Home Assistant requirements.
I don’t like SPOFs. Doing a SSD NAS + Hypervisor combo is kind of a SPOF, even with the rpi’s (assuming you go with root-on-nfs instead of alpine diskless install), but at least it’s a usable solution. The least I’m asking you is to power on your big server once a month to take backups of the new build you have, no matter if it’s going to be an h4+ / ultra, or anything else.
The H4+ and Ultra have an intel GPU, which support quicksync.