Do you mean a piece of the reaction wheel getting thrown across the room? You could shield that with something like they do on jet engines to avoid turbine blades being launched through the fuselage. I think the object itself is heavy enough compared to the energy in the reaction wheels that it would just fall over.

The cube? Not severe but enough to definitely wear safety glasses when things are activated in development. The couch? That's a fair amount of mass at a good height above floor level; definitely don't want to drop it on your body parts. Tje reaction wheels failing, Calc the max velocity & mass of the ring, and that'll give you an idea of the energy levels you're dealing with. I see nothing that would prevent me from doing either project, just enough to take good ordinary safety measures. Start on much smaller projects, enjoy the builds, and by the time you get to the cube & couch, you'll be able to estimate all that you need.

Also, when you have a question in development, remember: One test is worth a thousand opinions (especially re. your own opinions).

You can also make them in the shape of a mighty cheese:

https://youtu.be/BTrgdhq0vTw?t=72

Even the sorting by color would be useful if Van Halen was still touring.

https://m.youtube.com/watch?v=_IxqdAgNJck