If the developers aren't too lazy and immediately create unique visuals for all characters, that would be just great!
I don't think they will bother with that.
Will Heroes from the same faction, belonging to different races (e.g., Medusas and Minotaurs), have different models on the adventure map?
Currently, each faction has two models (one for Strength heroes, the other for Magic heroes), which are a collective image of the inhabitants of that faction and most of the races found there.
Will the hero's model correspond to their gender?
Currently - no.