Depends on the individual and how set you are in your ways and how open you are to new/old ways

Hard to say; but once you get past the base information and it's application (like shields = don't get hit from arrows, morale is determined by an average of the units in the squad and size, etc) then you get into the fun aspects of playing as opposed to just sort of trundling along.

The first hump is usually learning the interface and using it easily (via hotkeys).

The second hump is learning what is 'good' vs what is 'bad' and what is effective vs you losing (units, battles, games) without knowing why.

The third hump is finding your playstyle and how to balance the many many ways to play with how you enjoy playing effectively.