Help for SFF NAS in Node 304 with ECC ram

[HotPlot]

Hi all,
I would like some help/feedback on an upcoming build I’m trying to piece together. A similar build here but not quite the same components nor usage.

 

Usage :
plex for movies, tv shows and store all my data in general + regular backups of my PC & smartphone

 

Goals :

1. small form factor in a good case => Node 304
2. data integrity for as long as possible => RaidZ2 + ECC memory

With these two criteria, the choice of motherboards got very small. In my country (France), it seems that the only board I could buy online is an ASRock Rack X570D4I-2T. I don’t mind the price, especially for such incredible specs (IPMI, 10GB Ethernet, etc.)

 

Build so far :

• Node 304
• 6 x Ironwolf 4TB
• ASRock Rack X570D4I-2T
• Ryzen 5 3600
• 16GB (2x8) SODIMM ECC 2666MHz (Kingston KSM26SES8/8ME)
• Some gold or plat PSU, probably 400-500W

Have doubts about:

• Memory : is 16GB enough or should I go 32 ? I know that ZFS eats a lot of RAM and I want my NAS to be future-proof if I ever need a VM someday or something alike. Also, I suppose that the more RAM, the more writing cache.
• HBA : in a video from Gamers Nexus, Wendell said that he had a bad experience with on-board sata ports on an ASRock Rack X470D4U2-2T and thus he recommended to add a HBA card in PCI-e. On the contrary, I read here that integrated Intel and AMD HBA’s are fine. Should I go for a dedicated HBA card like a LSI SAS9211-8I or plug all 6 drives to the two OCulink ports ?
• Caching : since there might be a NVME port on the motherboard, should I use it for caching or rely more on RAM ? What other use of the NVME drive could I have ?
• CPU Cooler : is apparently a pain in the butt because of the pre-installed backplate with Intel 1156-style mounting holes on a AM4 socket. Workarounds are proposed here, but I’m kinda scared of force-threading M3 screws or tearing off the plate on a 445€ mobo.

I would appreciate any feedback about anything stated above, especially the doubts. Thank you !

PS: you might also see the same post in a couple other forums. Please understand I’m not spamming, but just trying to get a maximum of feedback ^^’