I really doubt that hoarding cash would cause recessions. That's up for debate obviously.
Yes, even im not sure about this. Its Keynesian and lets be honest, most of us are tilting towards the Neoclassical/Austrian school of thought
The issue remains that Bitcoin can't be a "medium of exchange" or "unit of account" until price volatility stops.
If we justify hoarding as "the smartest thing to do" -- then we have bigger problems. Lets agree that its the ONLY thing to do instead of pretend this is a strategy that clever people are employing.
The issue will arise - the world has never worked with a non-inflationary currency before. Hoarding will affect circulation - the question is how will this be dealt with and is it the responsibility of the currency or the people.