> In general a series of positive integers might start counting from 0 or from 1 there is no way to know up front.

No. Positive means precisely greater than zero.

> Tight coupling is good.

No. It depends, usually because decoupling has cost.

> By spending 50% of your time NOT writing prod code (but tests instead) you can INCREASE your velocity.

...as well as decrease the velocity for all the rest of your team by stiffling the architecture with tests. Depends on what and how is written.