In general, I focus on library size, not concurrent usage, as the thing that should drive hardware choices. To a certain extent the type of audio content you’re playing (particularly high-res PCM and DSD) and whether your output devices require format conversion (especially DSD->PCM conversion) could come into play if you were doing a lot of streams at once.
I do not recommend making overly constrained hardware choices like Atom, Celeron, machines with <4gb of RAM, machines that will put Roon’s databases on a spinning disk, and so forth.
We don’t artificially limit TIDAL playback on our end, but we are not in a position to comment on their legal obligations to the copyright holders or the rules that are enforced on their side, so I’m going to leave that one alone.