Thank for the response!
- What parameter shows max current for base?
- If I know target collector current, should I use Hfe curve to find correct Hfe value?
- Are darlington transistors really have only on and off states due very high gain or partly on state is possible?
You are using 'open' in a confusing way - a current switch is open when it carries no current (the opposite from a water tap. Closed circuit - current can flow, closed tap, no water can flow...
Yes, I was unclear, but you understand me right.
Fully saturated transistor = closed switch (current flows), closed transistor -- opened switch (no current).