Spinning myself crazy regarding upgrade

This is probably too long for most people, but I’m looking for advice. My problem is having 3x machines that have 8th gen cpu and only one is being used to its potential.

Current hardware:

-8th gen i5 using Windows Server in mini-itx case with 3.5’s holding 50tb of audio-video. This is also my Plex server. It has 1 PCIe 3.0 x16 (currently in use with pcie ssd that is for random cache and file sorting business).

-NK 4.0 with 12x3.5’s that is my backup for everything. Uses PCIe 2.0, currently with LSI 9217-8i. It runs Xpenology which is stable but severely limited due to its age.

-One HP 290 sitting around with its 8th gen Celeron. Has PCIe 3.0 x16.

-Synology 1515+ that is mostly used for auto-backup of wife stuff. It is destined to die from the C2000 bug.

Slowly creating a new machine:
-8th gen i5
-ATX mobo with PCIe 3.0 x8/x8. Also has 6xSata or 4xSata + 2x NVME. Default NIC is 2.5gbe
-Dell SAS3 8i HBA in the mail that will need flashing
-Intel 8x2.5 SAS3 enclosure for 2x5.25 bays. This creates a headache for rack-chassis searches. Hopefully the new Rosewill will be affordable and available.

On the sidelines:

-One HP N40L (7th gen Microserver) that can surprisingly do a lot with it’s 4-6 HD capacity and PCIe 2.0 slot. Can run practically any OS
-Two Mellanox 40gbe cards that could be direct attached to each other.
-One 2.5gbe PCIe x1 and one 2.5gbe USB dongle
-Spare laptops and mini clients that can run any OS
-Brocade ICX7450 with 4x10gbe and 2x40gbe. It’s in a rehab status because the 2.5gbe’s on it aren’t functioning and I’m monkeying with the electrical in it.

My needs:

Plex makes my world go round. I only stream inside the house; one TV uses wifi. My projector is within wire distance of my server collection, so whatever device I use to connect to the projector can probably use direct stream.

NFS/SMB for home laptop, ipad and phone backups. Pretty much keep something like Owncloud so that I have WAF for her stuff. The beauty of the synology is its ease of backup. If I weren’t facing its inevitable death, I think my choices would be easier.

I don’t need Windows for these things, but have all types of keys if needed…

My goals:
-Continue the 2xredundant backup I have in place. (Currently the mini itx and synology backup to NK 4)

-Put in place something that can run more advanced features, such as remote/distributed gaming, retro gaming emulation, VM if needed, etc.

-Go fast. I have some SAS3 items listed above, and have fast network stuff on the sidelines also. The fast network stuff is only for the benefit of direct-attached items since my house has inaccessible cat5e cables going to only a few rooms.

My problem that I’m wrapping my head around is, what’s the best use of the big three: the current i5 in itx mobo, the HP290, and this new machine. I can swap the cpu’s between any of these (if I have to). I could put the HP290 together as the retro-arcade machine, since it seems Dolphin will run on the i5-8600. The HP290 could sit next to and connect to my TV (no LAN wires running to it, only wifi).

I am looking at putting Unraid on this new machine I’m creating. That gives me 8x 2.5 sas3, with 40gbe NIC. Then I would attach the other 40gbe card to the other i5 that has Windows (which would keep my movies duplicated). I could keep NK4 together as cold storage (now triple the movies, which seems unnecessary).

But, two i5-8000’s running file-serving doesn’t seem optimal.

For the Synology 1515+ - I think soldering a resistor between two pins may keep it in action - Synology DS1515+ Intel C2000 Bug Fix(1) - YouTube

yes, it would fix that or slow it down to the point where the bug will take longer to hit. I’m not the soldering type (yet?), so I’m seeking overpowered options like the i5-8600