I seriously doubt we are even that much. I would say 1M and that's a great number as well (what I am trying to say it's just that I hope it's not lower).
As for the Bitcoin volatility and change in price, yes, we are still very small and price is influenced very easyily. As we grow in the future(hopefully), price will be getting more stable. Bitcoin is pretty much behaving just like any other currency, asset, commodity. All of this is quite normal.
You are correct the reason behind high fluctuation is low demand and lower supply which make big gamblers to play high with buying and selling in the market, but who are in investing mode they can go for buying in lower and wait for the high price so that they can sell,
all the products which have joined in commodity trading they all show high volatile in market price due to lower supply and gamblers playing highly with the prices.