Re: How stable (or not?) is Rawhide?
I don't think this can be answered except anecdotally. So, anecdotally, I've had times I couldn't install it. Other times it ran decently for a few weeks before annoying me.
What's going on with the upstream packages in Rawhide will have an impact. Obviously, if you use packages of reliable products that see little or no change from upstream, you'll probably have a smoother ride than if you use something that's in rapid development.
Also, every so often Fedora jumps into a Big New Thing during its development cycle. Like systemd or a brand new installer, the first release of Gnome 3, etc., well before they see the light of day in any other distribution.
My understanding of Tumbleweed is that it's something of a periodic snapshot that does undergo, as an entity, some amount of testing before release. I don't believe this happens in Rawhide. That begins after it's branched.
I often jump into new Fedora releases early in the alpha stage. Stuff happens, but usually they've been usable enough to stay with.