This does not consider the different usages of storage. Roon disk I/O for its databases makes a larger performance difference than anything else you can upgrade. then CPU, then RAM. That EVO NVMe will give you better latency on those DB reads/writes.
Our official statement on this is:
1) Run Linux if you can
2) run the fastest SSD you can find for the DBs (64gb for the database SSD should serve almost everyone)
3) put your audio files on the cheapest, quietest, and most reliable storage you can find. (5400rpm NAS drives?)
Your NUC purchase is in my opinion, better than 99% of Roon setups out there. It is almost exactly what I am running at home (but I have only 4gb RAM since that’s all I need).
I run a super trimmed Linux that we call RoonOS (~40 MEGABYTES!)… the idea is to make this an OS we can provide Roon Core partners. It boots in about 2.5 seconds, which I’m trying to get even faster.
As for i3 vs i5 vs i7 – I think the i7 generates too much heat, and the i5 is a great CPU. The i3 should serve most people just fine, but you can’t go wrong with the i5 if you aren’t price sensitive.