You got it quite well :)

Have fun with the build

Yeah, but even if they seems to be contradictory messages, they are not.

RAM is always the first resource that is depleted is a nas/homeserver built, more ram or the possibility of expanding the ram is always a safe bet. But for a nas or a non Realtime system ddr4 is also not mandatory.

Reduce the cooling goes into the direction that the system is not going to be under high cpu load, so no need to dissipate, you can even reduce the cpu.

SSD is not necessary for a nas but it will make you VMs or containers snappier.

So coming back to the subject, your cpu is overkill, and therefore your mother board too (it has even support for sli!), having more ram is always good but my opinion is with 16gb you are good to go for a good amount of time (my server runs on 8gb and I don’t experience any problem yet), obviously, your cooling needs to pair your cpu tdp.

SSD or m2 memories are cheap additions, and like somebody else suggested, it is good to have many pci slots even if they don’t go full speed (x16) but will give you the flexibility to add more sata ports or Ethernet connections on the 10gb.

Honestly, if budget is not a concern you can not be mistaken with this built, but I can see potential to spare like 100 bucks in hw and another 100 in bills in next years

Honestly, I have the impression your setup is oversized (knowing nothing about what you want to run)

NAS systems set on idle like 90% of the time unless your are doing really crazy things with de duplication and distributed iscsi for super big volumes, that I have the impression your are not going to do.

You can probably cut the performance/specs to the half and still being good for the following 10 years and the extra that you will save on electricity too.

As a comparison I checked this built against your synology and in the multicore setup is x10 more powerful (https://www.cpu-monkey.com/en/compare_cpu-intel_celeron_j4025-vs-amd_ryzen_5_5600x)

Just my two cents