I've been looking at NUCs recently, but I can't decide how much compute power I should aim for. What NUC did you buy?
It's got a DDR3 ram slot and can host 8GB ram, along with a sata port and a slot for a 2.5" disk. It also has 4GB of on-board storage that I really don't care about.
The processor is a single-core atom that clocks at about 1.4GHz with a TDP of about 5W.
I don't really care much about speed for this machine because it will become a home vpn gateway running PFSense. The CPU has AES-NI instruction, and that's what convinced me to get it.
My current vpn gateway is a Dell Optiplex FX160 which is still an atom and performs okay-ish, but has got no AES-NI and no internal storage beyond a dumb 2GB disk-on-module, on which pfsense barely fits and consumes about ~17 Watts powered on.
If you're optimizing for price and power consumption get an older SKU with an Atom, if you want more horsepower anything 10th gen with 4 cores will handle just about anything you can throw at it, and the idle power consumption is quite good too.