I would use the 250 GB version for the OS drive. Why spend the money on something that will never be used, as only the database goes on that drive and it will not get big enough to fill a 64 gb drive.
I think that is desktop RAM not NUC RAM. NUC’s use laptop RAM. Might be better with something like…
As always, double check the compatibility with the memory and the NUC model.
FWIW I am going for a NUC8i3 over the NUC10i3. It’s all I need for my library with plenty of head room. I currently have around 73,000 tracks/ 5,000 albums. Adding a 128GB NVMe M.2 SSD and 8GB DDR4. There’s no need to over-spec these things.
I have multiple zones and use upsampling (power of 2) on some zones, cross feed on my headphone setup, and occasionally volume levelling and other filters.
Once your library is greater than 250k tracks does ROCK require more 8GB. So for most 8GB is sufficient and spending extra to have 16GB or more in a NUC to run ROCK is just a waste of money.