If I don't have my own library and I'm streaming Master from Tidal... Do I even need Roon? If I understand correctly, if I use NUC Wi-Fi with AirPlay or Apple TV, I'm back at the same quality that I would have from just using Apple TV or Fire Stick and Tidal, no?
If you run Roon on a single laptop, it’s both your server and endpoint - you connect your DAC via USB as you normally would. In that case the only advantage is that you can install Roon on your phone or tablet and use it as remote without you needing to somehow connect via AirPlay or Bluetooth. The remotes will automatically find the server in your network. No quality difference. (Obviously no need for Ethernet in this case since server is connected to the DAC).
With a NUC, you just avoid having that laptop running 24/7 and replace it with an efficient mini PC. Your DACs need to communicate with the server, if not directly via USB, cheap RPis via good WiFi do that just fine. When you turn on your DAC, the server is notified and the DAC shows up in all your remotes.
There are a few alternatives to RPi, checkout the DietPi website. I’m 99% sure every ARMv7 or ARMv8 machine will install the Roon Bridge. You might want to double check though.
But yeah, play with it for a while. If you like the interface and recommendations you get, you can figure out the multi room stuff later.