> That amount is different for every kind of business.

Yes it is, but we could define it algorithmically. Perhaps 5x the median of the last 5 years of operational expense? That would essentally say "you can run with no revenue for 5 years on this pile of cash, that's enough of a rainy day fund."

> Furthermore, putting cash into the market by force is basically just inflation isn't it?

No, you are perhaps thinking about "printing" money. Which is that money is injected into the economy instead of having it being generated by the economy.