I'm planning to purchase a Synology DS1621+ to use as my primary storage drive for a large photo catalog. I plan to use 4 x WD Ultrastar drives in RAID 10. I'd like to edit directly off the NAS, so I will upgrade to 10GBe via PCIe. Hoe much (if at all) would my use case benefit from upgrading M.2 NVMe and/or RAM? Thank you.
An excellent choice with a NAS.
Adding SSD cache on a DS1621+ would give a small speed boost. But you would only notice the difference if there were 5 or more users editing. The cache option simply keeps a copy on an SSD with frequently accessed files. If you would work on the same files all the time, then you would notice a speed increase. But single image editing will unlikely be improved.
Adding more RAM only helps if you are low on RAM memory. Otherwise, if you simply have lots of |RAM - doesn't improve things.
I hope this helps.