Easy money is most closely represented by the 3rd item you listed. It's almost impossible to lose with a 0% rate, as you can use it for even highly conservative investments that might return 2% and be nearly guaranteed profit. Gov't takes all the risk and banks keep all the profit.

It's almost impossible to determine when there's excess in a modern economy of sufficient size. There are so many variables and changes take a long time to propagate through an economy. By the time the metrics used to observe an economy and decide how to manage it finally produce recognizable results, there are major distortions. That makes any actions taken more likely to cause harm and further disruption than correct any imbalances in the first place.

In order to truly be able to centrally manage an economy, massive amounts of data must be collected, increasing complexity and potential for errors. The task becomes herculean while allowing the system to manage itself would result in the distortions and imbalances resolving themselves over time.

There are many factors that influence growth rates. Yes, the human aspect among others. Raw resource availability, energy production, global competition, population growth, infrastructure development, etc...