What variables must be considered before making any investment decision?

This is a multi-variable question with a similar menu of complex solutions. Some of the variables to consider, among others, would be (1) The actual objective, (2) Time Frame, (3) Risk aversion, (4) Understand the business or asset class, (5) Have an exit strategy and plan.

What would be the minimum basic concepts in financial markets that must be clearly understood in order to move forward in understanding deeper concepts in the variety of existing markets such as commodities, equities, bonds, derivatives, forex, etc?

The understanding of (1) Cost of Money and how it works , (2) Future Expectations, (3) Risk Management, and (4) Supply & Demand would be an excellent combination to get started.

What is the most crucial step in the roadmap to startup a business?

Definitely the jump from (1) having a good idea to (2) have it structured and implemented via a digested and controlled step-by-step planning to make sure we walk the talk. Such jump is even crucial to determine whether it is just a good idea or it is a good idea with huge business and market potential.