Home-Server Upgrade Recommendations

Hi, could you help me and recommend a good upgrade for my (dated) home server?

I'm currently running Unraid on an ASRock H97 Pro4 and an Intel Xeon E3-1231 v3, together with 24GB DDR3 RAM, a NVIDIA GTX 960 (for hardware transcoding) and a few old, mismatched HDDs. I chose this hardware mostly, because it was cheap/easy to get or I had it laying around. The server is primarily running Plex and the *arr-Stack, as well as smaller, less demanding applications and is showing it's age. I also want to add a VM for my wife or occasional guests to game on. Because of this, I think it's time for an upgrade, but I'm not really sure, what hardware to choose.

My current requirements would be the following:

• Should be able to run the following applications easily
  • Plex (2-3x 1080p should be enough, but a little bit of overhead can't hurt)
  • Sonarr/Radarr/SABnzbd
  • Tdarr Server + Node to transcode new media in the background; this is mostly for space savings. I'm currently running the node on my gaming PC, but want the server to do this in the background 24/7
  • overhead to do a little bit of tinkering and running smaller applications; I think, most of the load will be from Plex, Tdarr and the other *Arrs
• At least 6 SATA connections OR extra space for an adequate HBA card
  • I want to connect 3-4 Drives and have the possibility of adding some later; Querstion: What drives would you recommend? At least 10GB per drive. Im currently looking at 3x WD Red Plus 10 TB (one as parity).
• 2 M.2 slots
  • a dedicated cache drive (for IO) as well as a drive to put the VMs/Appdata onto; Question: Is this even needed, or would one (bigger) SSD be enough?
• dedicated GPUs for Plex/Tdarr hardware transcoding as well as gaming so I can assign each to the relevant VM (one will probably be windows)
• be future-proof so I don't have to upgrade again in a few years
• adequate power consumption (assuming an idle state without active gaming or transcoding); I also want to reuse the 500W be quiet! Pure Power 11 CM I already got.
• fit in the Fractal Design Define R5
• 1GB ethernet
• be as quiet as possible
  • I already got noctua case fans and will probably throw an NH-D15 on the CPU

I'm especially unsure regarding the choice of Motherboard, CPU and GPU(s). I looked at the X570 FTW WIFI ATX Motherboard with a Ryzen 5800X to get good, future proof processing power and all the features I need, but am absolutely unsure if thats overkill or not. As GPUs I chose two GTX 1660 Super (for now), because I found recommendations for this card for transcoding as well as playing current titles on medium to high settings. Here I'm unsure if it is overkill for transcoding and maybe a bit dated for current gen gaming.

If possible, the parts should be buyable new, as thats way easier for me, than hunting on the used market.