It was many years ago that RST caused problems for Primocache, but it didn't last long after I sent a report into Romex support. They squashed the bug/problem in about 36 hours. I've heard confirmation recently from them that it poses no problem at all.
What is your strategy for using Primocache on the server? With 8GB of RAM you won't have a lot for a L1 cache, but it seems like you devoted a 120GB SSD for a L2 cache (which should help quite a bit). Do you plan on caching the RAID 5 array with the SSD? It's a large enough array that you may get low hitrates if a lot of data resides on it.
One thing I'd suggest as a change to architecture - don't use RAID 5. It's outdated, and not nearly as reliable as it used to be on large drives (rebuilds stand a chance of failing, crashing the array and making it unrecoverable). Instead I'd use drive pooling software like
Stablebit DrivePool. I use that on my home server (9x8TB drives and 4x4TB dual-parity drives). You can add drives on the fly to the pool, and a ton of other neat stuff.
When you couple Drivepool with on-demand parity calculation software like
SnapRAID, you get the best of both worlds: re-compute parity with a simple powershell script command, recover individual files or entire drives, scrub the parity against the data to verify parity integrity, many levels of parity (up to 7 I think), etc.
You can of course still do RAID 5, but I think the ship has sailed on that architecture for the most part. I used it for many years, even on an old WD MyCloud EX4, but finally retired all use of RAID in favor of drive pooling and on-demand parity generation.
I'm a little split on using Server 2016 for a home media/file server - they removed some things from it, and you just don't gain a lot for the extra cost and administration hassle. Mine is still running Windows 7 x64 believe it or not, and doing very well. If I had to upgrade the OS, I'd probably go with W10, and simply disable all telemetry.