Is Roon a good substitute/upgrade for iTunes Match? If I download my library into iTunes on my Mac just once, can I upload it all to the Roon cloud and keep in there forever, or do I still need local storage?
No. There is no “Roon Cloud” for library storage. You would need to store locally and/or subscribe to Tidal or Qobuz. I would be nice if Roon offered a cloud storage option which could enable mobile use. But right now, there is no cloud storage, nor is there a mobile Roon option.